The Kolmogorov-Smirnov test is used in this paper to test the distribution of month-scale number of small earthquakes occurred in the Longmenshan fault, Sichuan, China. The results show that the distribution of the semi-anual number for ML≥3.0 earthquakes occurred since 1970 agrees with normal distribution, and that of the monthly number for ML≥2.0 earthquakes occurred since 2000 agrees with the Poisson distribution. Analyzing further the changes of distributions of the monthly number and the semi-anual number with time, it is found that before the two earthquakes with MS5.0 in September and November of 1999 and the Wenchuan MS8.0 earthquake, the distribution of the semi-annual number for ML≥3.0 earthquakes changes abnormally, and the distribution of the monthly number for ML≥2.0 earthquakes changes obviously prior to the Wenchuan MS8.0 earthquake.