Abstract: A laser radar ranging system based on the Michelson interferometer was designed using the difference-frequency interference principle. The system can realize three-dimensional shape measurement with the shaft encoder.The design of the laser radar launching system and receiving system was introduced .For the launching system, according to the Gaussian collimating theory,the relevant parameters of the optical system were determined,and a laser ranging system used for 2m~18m range was designed. At the same time, the zoom curve was drawn by using Zemax macro programming. For the receiving system, the relevant parameters of target were determined based on the laser radar ranging equation to get the maximum energy of the echo, and the echo beam was coupled into the fiber through the optical system. This system realizes the launch and receive common-path. It can be used for noncontact measurement of bullet head face of railway vehicles and other complex three-dimensional faces. It has the features of high speed, high accuracy, and has very broad prospects for development.