A probability distribution model for the light log-intensity fluctuation in turbulent atmosphere was introduced by taking consideration of the skewness and the kurtosis. The model is suitable for fitting the probability distrbution from experimental data. It was found experimentally that under the weak fluctuation condition the probability distribution is close to a normal distrbution when the turbulence is well deveploped, otherwise the ditribution will deviate from the normal distribution and the skewness of the log-intensity probability distribution is alwsys negative and the kurtosis positive.