As LD rangefinder cannot meet the requirements of miniaturization and far ranging at the same time,digital signal processing method based on coherent integration and correlated detection is presented.Ranging performances of different pseudorandom codes and m sequence was compared by using delay method.The simulation results show that the ranging with m sequence has better ranging accuracy and SNR under the condition of 10 W peak power.The research result can help to improve the ranging performance of LD rangefinder.