TianQin is a proposed space-based gravitational wave detector operating in the millihertz (mHz) frequency range. The mission involves a constellation of three drag-free spacecraft orbiting the Earth, using inter-spacecraft laser interferometry to monitor distances between test masses. The goal is to detect gravitational waves from a single, well-understood source with high confidence within a few months of observation. The mission is designed to be technologically feasible, with a focus on optimizing the laser interferometer and disturbance reduction system to detect signals from a single reference source, such as the binary system J0806.3+1527, which is a strong candidate due to its short orbital period and proximity to the Sun. The spacecraft will be placed in nearly identical geocentric orbits, forming a nearly equilateral triangle, to minimize operational costs and improve sensitivity. The mission aims to achieve a signal-to-noise ratio (SNR) of 10 in three months of observation, with a sensitivity goal of 1 pm/Hz^1/2 for position and 10^-15 m/s^2/Hz^1/2 for residual acceleration. The project is expected to be launched in the second half of the next decade, with a cost estimated at USD 550-800 million. The mission will use time delay interferometry and advanced technologies to reduce non-gravitational noise and achieve high precision measurements. The preliminary error budget for the key components, including the laser interferometer and disturbance reduction system, has been estimated, and the current status of these technologies is reviewed. The project aims to provide a direct detection of gravitational waves and advance the field of gravitational wave astronomy.TianQin is a proposed space-based gravitational wave detector operating in the millihertz (mHz) frequency range. The mission involves a constellation of three drag-free spacecraft orbiting the Earth, using inter-spacecraft laser interferometry to monitor distances between test masses. The goal is to detect gravitational waves from a single, well-understood source with high confidence within a few months of observation. The mission is designed to be technologically feasible, with a focus on optimizing the laser interferometer and disturbance reduction system to detect signals from a single reference source, such as the binary system J0806.3+1527, which is a strong candidate due to its short orbital period and proximity to the Sun. The spacecraft will be placed in nearly identical geocentric orbits, forming a nearly equilateral triangle, to minimize operational costs and improve sensitivity. The mission aims to achieve a signal-to-noise ratio (SNR) of 10 in three months of observation, with a sensitivity goal of 1 pm/Hz^1/2 for position and 10^-15 m/s^2/Hz^1/2 for residual acceleration. The project is expected to be launched in the second half of the next decade, with a cost estimated at USD 550-800 million. The mission will use time delay interferometry and advanced technologies to reduce non-gravitational noise and achieve high precision measurements. The preliminary error budget for the key components, including the laser interferometer and disturbance reduction system, has been estimated, and the current status of these technologies is reviewed. The project aims to provide a direct detection of gravitational waves and advance the field of gravitational wave astronomy.