A wireless optical transmission experiment with a link length of 610m was carried out at night in Lanzhou area to investigate the statistical characteristics of light intensity fluctuation in sunny, overcast, sleet and dust days. The atmospheric structure constant of refractive index C2n in different meteorological conditions were measured by using the scintillation method. The measured maximum, minimum and mean value and the standard deviation of C2n indicate that the range of C2n is 1.06×10－15 m－2/3~1.05×10－13 m－2/3 of the experimental period, which belongs to moderate turbulence. Moreover, it also indicates that the fluctuation of C2n in sunny day and sleet day are greater than overcast day and dust day. Furthermore, Rytov variance is analyzed by using the measured light intensity values. The results show that in sunny day, sleet day and dust day, the light intensity fluctuation belongs to weak fluctuation at most of the time and there is a small part of the time it belongs to moderate fluctuation. However, the light intensity fluctuation in overcast day belongs to weak fluctuation in all time. The light intensity fluctuation in sunny day and sleep day are greater than overcast day and dust day. We can conclude that the probability distribution of light intensity in different meteorological conditions is closest to the exponential weibull distribution by comparing the nonlinear fitting results of the logarithmic normal, Gamma-Gamma and exponential Weibull distribution. The goodness of exponential Weibull distribution is greater than 0.989 95. In the weak to medium fluctuation region, the Gamma-Gamma distribution fits better than the lognormal distribution.