In modern science and technology, LiDAR plays a key role in automatic navigation, industrial mapping and other fields, but the traditional phase ranging system has many problems such as low measurement accuracy and complex structure. A new high-precision phase laser radar ranging system is proposed in this paper. The system adopts the phase difference detection method of laser control with the same frequency reference, including the optical structure optimization of the laser transmitting and receiving modules, and the amplification filtering and differential mixing processing of the receiving circuit, and finally produces a high-resolution phase discrimination system based on AD8302. The experimental results show that the measurement accuracy of the system is millimeter level, which is simple and practical and can meet the needs of a wide range of practical applications. This research provides a feasible solution for LiDAR technology in high-precision distance measurement.