3D imaging lidar based on half-square to square correlation method is proposed.The architecture of the system and the principle of phase ranging algorithm are discussed with Matlab simulink.The imaging precision is also analyzed.The simulation shows that this algorithms and principles are correct and effective.The modulation depth is greater than 1.2.The simulation verifies the work theory of scannerless 3D imaging lidar.It is useful for the research and design of the practical 3D imaging lidar.