This paper reviews the development and applications of unmanned autonomous intelligent systems (UAIS) in 6G non-terrestrial networks (NTNs). UAIS, as a physical form of artificial intelligence, have gained significant attention for their applications in autonomous driving, logistics, surveillance, and medical services. With the rapid evolution of information and communication technology (ICT), 5G and beyond-5G communication have enabled numerous intelligent applications through the comprehensive utilization of advanced NTN communication technology and artificial intelligence. To meet the demands of complex tasks in remote or communication-challenged areas, there is an urgent need for reliable, ultra-low latency communication networks to enable UAIS for applications such as localization, navigation, perception, decision-making, and motion planning. However, in remote areas, reliable communication coverage is not available, which poses a significant challenge for intelligent systems applications. The rapid development of non-terrestrial networks (NTNs) communication has shed new light on intelligent applications that require ubiquitous network connections in space, air, ground, and sea. However, challenges arise when using NTN technology in unmanned autonomous intelligent systems. The paper presents a comprehensive analysis of the opportunities and challenges of unmanned autonomous intelligent systems in UAV NTN, along with NTN-based unmanned autonomous intelligent systems and their applications. A field trial case study is presented to demonstrate the application of NTN in UAIS. The paper also discusses the role of UAVs in NTNs, including their use as users, relays, and base stations. It highlights the importance of UAVs in providing flexible and ubiquitous network coverage for UAIS in remote areas. The paper also discusses the challenges and research opportunities of UAVs in NTNs, including the need for distributed computation architectures for computationally intensive tasks and massive data offloading. The paper concludes that the development of 6G NTN technology is crucial for supporting UAIS with low-latency, high-bandwidth, and multi-access edge computing in complex environments. The paper also discusses the applications of UAVs in NTNs, including material delivery, air traffic control, and disaster relief operations. The paper emphasizes the importance of UAVs in providing communication coverage for ground users in remote areas where terrestrial infrastructure is unavailable. The paper also discusses the challenges and research opportunities of UAVs in NTNs, including the need for efficient trajectory planning and control, as well as the integration of communication and sensing in future 6G technology. The paper concludes that the development of 6G NTN technology is crucial for supporting UAIS with low-latency, high-bandwidth, and multi-access edge computing in complex environments.This paper reviews the development and applications of unmanned autonomous intelligent systems (UAIS) in 6G non-terrestrial networks (NTNs). UAIS, as a physical form of artificial intelligence, have gained significant attention for their applications in autonomous driving, logistics, surveillance, and medical services. With the rapid evolution of information and communication technology (ICT), 5G and beyond-5G communication have enabled numerous intelligent applications through the comprehensive utilization of advanced NTN communication technology and artificial intelligence. To meet the demands of complex tasks in remote or communication-challenged areas, there is an urgent need for reliable, ultra-low latency communication networks to enable UAIS for applications such as localization, navigation, perception, decision-making, and motion planning. However, in remote areas, reliable communication coverage is not available, which poses a significant challenge for intelligent systems applications. The rapid development of non-terrestrial networks (NTNs) communication has shed new light on intelligent applications that require ubiquitous network connections in space, air, ground, and sea. However, challenges arise when using NTN technology in unmanned autonomous intelligent systems. The paper presents a comprehensive analysis of the opportunities and challenges of unmanned autonomous intelligent systems in UAV NTN, along with NTN-based unmanned autonomous intelligent systems and their applications. A field trial case study is presented to demonstrate the application of NTN in UAIS. The paper also discusses the role of UAVs in NTNs, including their use as users, relays, and base stations. It highlights the importance of UAVs in providing flexible and ubiquitous network coverage for UAIS in remote areas. The paper also discusses the challenges and research opportunities of UAVs in NTNs, including the need for distributed computation architectures for computationally intensive tasks and massive data offloading. The paper concludes that the development of 6G NTN technology is crucial for supporting UAIS with low-latency, high-bandwidth, and multi-access edge computing in complex environments. The paper also discusses the applications of UAVs in NTNs, including material delivery, air traffic control, and disaster relief operations. The paper emphasizes the importance of UAVs in providing communication coverage for ground users in remote areas where terrestrial infrastructure is unavailable. The paper also discusses the challenges and research opportunities of UAVs in NTNs, including the need for efficient trajectory planning and control, as well as the integration of communication and sensing in future 6G technology. The paper concludes that the development of 6G NTN technology is crucial for supporting UAIS with low-latency, high-bandwidth, and multi-access edge computing in complex environments.