In order to improve capability of a fiber coherent light detection and ranging (LiDAR), antenna characters were analyzed with modeling method. Based on the principle of backward propagating local light, the influence of antenna aperture on signal-to-noise ratio was discussed, and the influence of pupil truncation ratio on antenna efficiency was analyzed. The definition of coupling efficiency was proposed, and the influence of atmospheric refractive constant on d coupling efficiency and range was researched. By building experimental platform to obtain signal to noise ratio and frequency spectrum intensity in different distance gates, the simulation results were verified. The results show that when the range changes from 7km to 10km, the optimal antenna aperture and pupil truncation ratio were 100mm and 0.8, respectively. Moreover, compared with weak turbulence, strong turbulence makes range decrease by 30% for the same system. The research has important theoretical significance and practical value for optimized design of antenna.