A Rayleigh-Raman-Mie lidar (RRML) signal detection and optical receiver unit is constructed,the principle of lidar design is emphatically introduced,the design is based on the simulated calculation on atmosphere backscatter signal. The purpose of the signal detection unit is to improve the signal to noise ratio (SNR) of the lidar signal. By rational design the signal detection and optical receiver unit,use extremely sensitive R4632 photomultiplier tube (PMT) and photo counting method,a good SNR of Raman and Rayleigh signal could received. Through construct the PMT gating control and signal attenuation unit,a linear detection of aerosol and cirrus signal is received. Finally,the experimental result shows the rationality of the signal detection and optical receiver unit design method.