Abstract: Cloud base height (CBH) plays an important role in weather forecasting and flight service. However, CBH data with high spatiotemporal resolution are lacking. This study evaluates the CBH product of ERA5 reanalysis data using ground-based observations in eastern China, revealing the CBH feature in China through validated CBH data from ERA reanalysis. Overall, CBHs from ERA5 reanalysis data are lower than those from ground-based measurements, in which low and middle clouds are overestimated and underestimated, respectively. Additionally, under precipitation conditions, CBHs from ERA5 data indicate a higher accuracy for low clouds than for clouds under a non-precipitation synoptic background and middle and high clouds. CBHs are lower in the daytime than at night, peaking at 0900 BJT and 2200 BJT over eastern China in the daytime and at night, respectively. Overall, monthly mean CBHs from ERA5 reanalysis are consistent with the ground-based measurements in autumn and winter. Revised CBHs of ERA5 data gradually decreased from the northwest to the southeast of China in 2010–2019. Furthermore, CBHs are lower over southern China, northeastern China, and the Tibetan Plateau compared to other areas. Over the Tibetan Plateau, CBHs are lower in summer and autumn than in spring and winter. Additionally, the desert region has a higher CBH in all four seasons.