Optical intensity signal fading caused by the atmospheric turbulence can severely impact the performance of free space optical communication systems. Large aperture scintillometer is used to test the turbulence effect over the road and sea surface environment. Based on the obtained refractive index structure constant, fading characteristics of free space optical communications are analyzed over these two different environments. The difference of refractive index structure constant under the road environment and the sea environment is analyzed, the result shows that the turbulence intensity of road environment is much stronger than the intensity of sea environment. The change characteristics of probability of fade of colimated Gaussian beam are studied under the two environments, when the scintillation indices are minimum, mean, and maximum, respectively. It shows that the degree of optical signal fading over road is more serious than the degree over sea environment. Fade threshold parameter is discussed when the probability of fade is 10-6.