In order to investigate the effects of atmospheric turbulence on laser communication, an experiment is carried out to research intensity scintillation which caused by atmospheric turbulence. 15,000-frame gray images which grabbed by high-speed camera every ten minutes are processed and analyzed. Diurnal variation trend of scintillation index in different seasons are provided in the experiment, and the probability density distribution of intensity scintillation are analyzed in detail. The results indicate that diurnal variation of scintillation index are different in seasons in the weak turbulence conditions. It's also indicate that probability density is lognormal when scintillation index is large, and probability density is normal when scintillation index is small.