Based on Kolmogorov and Rytov′s theory model and considering the effect of turbulence intensity on the performance of free space laser communication,a modified theory model used to depict the bit error rate(BER) in both weak and medium turbulence conditions is obtained,the influence of turbulent intensity and wavelength on BER in communication system is also simulated.It is shown that in medium turbulence field,the influence of BER is very obvious compared with weak turbulence.The system BER increases rapidly with the increase of the propagation distance and trends to saturation.With system′s BER below 10-9,the effective communication range in the weak atmosphere turbulence will be greater than that in the medium turbulence regime.Under a certain intensity of turbulence the longer the wavelength is adopted,the better the system performance is.The analytical results can be used to improve the performance of laser communication system.