Abstract: A statistical analysis is made of the measured distribution of fade slope of rain attenuation, measured at Haikou from the ChinaStar-1 at the frequency of 12.5GHz. The distribution of conditional probability density of fade slope shows that the positive and negative slopes are distributed symmetrically. The standard deviation of fade slope which is the only parameter in VandeKamp model is refitted to fit the cumulative distribution of fade slope and a new relationship of this parameter to attenuation level and time interval is proposed. By comparison with the VandeKamp model and Salonen model, the improved model obtains the best accuracy.