Abstract: The applicability of ERA-Interim and ERA5 reanalysis in the complex terrain area of Southwest China is compared based on the observation data of 513 ground meteorological observation stations. The results show that the applicability of ERA5 reanalysis data about surface factors (2 m temperature, precipitation,10 m wind speed and 10 m wind direction) is superior to ERA-Interim, In particular, ERA5 can reproduce 2 m temperature better in Central Sichuan an Eastern Yunnan, reproduce precipitation better in Sichuan, Chongqing and Guizhou, can reproduce 10 m wind speed better in Chongqing, Yunnan and Guangxi, and reproduce 10 m wind direction better in Sichuan and Guangxi. It should be noted that ERA-Interim is more suitable for 2 m air temperature and 10 m wind speed in Tibet. In terms of monthly applicability, the applicabilty of the two sets of reanalysis data in winter and spring is better than that in summer and autumn. ERA5 has better applicabilty to 2 m air temperature in summer and autumn (May to October), monthly precipitation, 10 m wind speed and 10 m wind direction of the year. In terms of daily applicability, the applicabilty of the two sets of reanalysis data to 2 m temperature and precipitation from afternoon to night is better than that in the daytime, and the applicabilty of 10 m wind speed and 10 m wind direction in the daytime is better than that in the afternoon to night. ERA5 is generally better than ERA-Interim for the simulation of 2 m air temperature, and precipitation at 00:00, 10 m wind speed and 10 m wind direction in most periods.