This article describes a groundbreaking experiment in quantum key distribution (QKD) using a satellite-to-ground system, achieving secure communication over a distance of up to 1200 km. The experiment, conducted using a satellite named *Micius*, demonstrated the feasibility of establishing a global-scale quantum network by leveraging the low loss and minimal decoherence of space-based channels. The satellite, launched in 2016, was equipped with a decoy-state QKD transmitter operating at 850 nm wavelength, and it successfully transmitted a key rate of over kHz to a ground station in Xinglong, China, over a distance of up to 1200 km. This achievement represents a significant improvement over traditional fiber-based QKD, which is limited to a few hundred kilometers due to high channel losses. The satellite-to-ground link achieved a channel efficiency that is up to 20 orders of magnitude more efficient than fiber-based systems of the same length. The experiment involved overcoming several technical challenges, including beam diffraction, atmospheric turbulence, and pointing errors. To address these, the team developed a high-precision acquiring, pointing, and tracking (APT) system, which ensured stable communication between the satellite and the ground station. Additionally, they implemented temporal and spectral filtering to suppress background noise and used a motorized half-wave plate for dynamic polarization compensation. The QKD protocol used was based on the BB84 protocol with a decoy-state method, which allows for secure key exchange even in the presence of photon-number-splitting attacks. The results showed a quantum bit error rate (QBER) of approximately 1.1%, consistent with expected background noise levels. After error correction and privacy amplification, the team successfully generated a secure final key of 300,939 bits, demonstrating the feasibility of long-distance secure communication. The experiment also highlighted the potential for future applications, such as connecting distant locations through a satellite relay, and the development of a global quantum network. The success of this experiment marks a crucial milestone in the realization of a secure, global quantum communication infrastructure.This article describes a groundbreaking experiment in quantum key distribution (QKD) using a satellite-to-ground system, achieving secure communication over a distance of up to 1200 km. The experiment, conducted using a satellite named *Micius*, demonstrated the feasibility of establishing a global-scale quantum network by leveraging the low loss and minimal decoherence of space-based channels. The satellite, launched in 2016, was equipped with a decoy-state QKD transmitter operating at 850 nm wavelength, and it successfully transmitted a key rate of over kHz to a ground station in Xinglong, China, over a distance of up to 1200 km. This achievement represents a significant improvement over traditional fiber-based QKD, which is limited to a few hundred kilometers due to high channel losses. The satellite-to-ground link achieved a channel efficiency that is up to 20 orders of magnitude more efficient than fiber-based systems of the same length. The experiment involved overcoming several technical challenges, including beam diffraction, atmospheric turbulence, and pointing errors. To address these, the team developed a high-precision acquiring, pointing, and tracking (APT) system, which ensured stable communication between the satellite and the ground station. Additionally, they implemented temporal and spectral filtering to suppress background noise and used a motorized half-wave plate for dynamic polarization compensation. The QKD protocol used was based on the BB84 protocol with a decoy-state method, which allows for secure key exchange even in the presence of photon-number-splitting attacks. The results showed a quantum bit error rate (QBER) of approximately 1.1%, consistent with expected background noise levels. After error correction and privacy amplification, the team successfully generated a secure final key of 300,939 bits, demonstrating the feasibility of long-distance secure communication. The experiment also highlighted the potential for future applications, such as connecting distant locations through a satellite relay, and the development of a global quantum network. The success of this experiment marks a crucial milestone in the realization of a secure, global quantum communication infrastructure.