Abstract: The performance of the kilometer scale operational model (GRAPES-Meso 3 km) for short-term precipitation forecast over complex terrain areas of the Sichuan basin, the Yunnan-Guizhou Plateau, and the highlands of the eastern edge of Tibet Plateau in southwestern China has been carefully evaluated in term of the rainfall amount and frequency. The model forecasts are verified against daily and hourly precipitation data observed in the summer of 2019 at thousands of surface stations in the same area. Results show that: (1) The model can reasonably capture daily rainfall distribution and diurnal cycle of summer mean precipitation as well as the key relationship between hourly rainfall frequency and intensity over the complex terrains. (2) Positive forecast deviations of summer daily rainfall amount (frequency) are obvious in the whole research region, and the largest deviations are centered in Sichuan basin with the bias of 1.1 times (0.3 times) of the observed values on average. Positive deviations of daily rainfall amount forecast in the complex terrains are mainly contributed by the forecast amount of heavy rainfall (above 25 mm/d) events. Positive deviations of frequency forecast are mostly caused by light to moderate rainfall events over Yunnan-Guizhou Plateau and by heavy rainfall events over other areas. Areas of heavy rainfall from forecasts are often larger than observations, with the highest occurrence frequency of 82.8% occurring in the eastern edge of the Tibet Plateau and the lowest of 53.6% appearing in the southern Yunnan-Guizhou Plateau. (3) In terms of diurnal cycle, positive biases of hourly rainfall amount (frequency) are the main characteristics, and large deviations mostly occur around the peak time of observed rainfall in the night for different terrain heights. Large biases of hourly rainfall frequency in areas below 1200 m elevation occur from the peak time of rainfall in the night to the noon time of the next day, which indicates that the over prediction of daily rainfall amount was balanced by unrealistically long precipitation duration or by false hourly forecasts within a day. (4) Based on the diagnostics, the obvious precipitation (amount and frequency) deviations of the model forecasts over Sichuan Basin are induced by the special coupling of the over prediction of southwesterly winds in the lower troposphere at the south-southeast Yunnan-Guizhou Plateau and terrain characteristics in the Basin and surrounding area.