Atmospheric turbulence can induce intensity scintillation,beam drift, wavefront distortion and polarization degradation of returned signal,which affects the spatial light coupling ratio of the detection system as well as the heterodyne efficiency,and as a result,the detection accuracy will be reduced.The signal to noise ratio (SNR) of the returned atmospheric backward scattering signal is calculated at different heights;also the atmosphe ric scintillation modulation factor is analyzed based on the Hufnagel-Valley model,and the near-surface intensity scintillati on variance is acquired.The method of pattern matching numerical integration is used to simulate the wavefront aberration,an d the space light-signal mode fiber coupling efficiencies at different heights are obtained.Based on the complex amplitude of the light field and the airy spot model on the detector surface,the effects of the space phase fluctuation on heterodyne effici ency are analyzed.Combined with CO_{2differential} absorption detection experiment data using a 20m-optical path gas cell,the CO _{2concentration} detection accuracy of this experiment setup is determined;and the effects of atmospheric turbulence on outdoor experiment are studied.The results show that the atmospheric turbulence will reduce system detection resolution by 1.21times,and through th e 20m optical path,the system resolution is changed from 424.83×10－6 to 514.04×10－6.This analysis is of import ance to the outdoor exp eriment of coherent differential absorption lidar (DIAL).