Abstract: Based on the three-source fusion hourly grid precipitation products from 2018−2022, the spatial-temporal variation of heavy rainfall on the east and west sides of Ailao mountain and its relationship with altitude in rainy season have been analyzed. The results show that: (1) The total precipitation of Ailao Mountain area is more in the southern and the western regions and less in the northern and the eastern regions during flood season. The moderate level rainfall made the higher contribution rate than other levels. Short time heavy frequency rainfall, in both sides of mountain, mostly happened in August. The maximum and high frequency periods did not coincidence. (2) The center of large precipitation located at the low altitude area in the south, and the center of small precipitation located at the high altitude area in the north. The total precipitation, night and daytime precipitations have a nonlinear relationship with altitude. Rainfall increases with the elevation of altitude, while the altitude exceeds 1200 m, precipitation decreases rapidly. The precipitation is higher in altitude 500 m, 1200 m and 1900 m. (3) On the east, the variation of light rainfall, moderate rainfall and heavy rainfall is consistent, while the rainstorm is quite different. The proportion of precipitation of each magnitude does not change significantly with altitude. On the east, only the small rainfall is positively correlated with altitude, while the other levels rainfall showed an irregular fluctuation. The proportion of precipitation of small and moderate increases with the elevation of altitude. (4) Both the frequency and extreme value of short-time heavy precipitation decrease with altitude elevation.