Abstract: The ISCCP (International Satellite Cloud Climatology Project) and NCEP (National Centers for Environmental Prediction) datasets have been exploited to investigate the vertical cloudiness over East Asia simulated by BCC_AGCM2.1 (Beijing Climate Center_Atmospheric General Circulation Model 2.1) and BCC_AGCM2.2. The sources of errors are also explored in this paper. The two models generally can well simulate the distribution of total cloud amount and vertical changes in cloudiness along the topography, however, the simulated cloudiness is less than observations. The cloud cover simulated by AGCM2.2 is less than that by AGCM2.1. Despite the better representation of complex terrain, AGCM2.2 does not show any advantages of the high resolution. The poor performance of the model in the simulation of circulation fields in eastern China leads to underestimation of cloudiness, particularly in the AGCM2.2 simulation. Meanwhile, the overestimation of relative humidity in the upper troposphere results in more simulated cloudiness than observations. The underestimation of relative humidity near the ocean surface and unrealistically small moisture content simulated by the model in Sichuan Basin and its surrounding area in the cold season lead to less cloud amount in the model result. The simulated cloudiness is sensitive to relative humidity. The response of cloudiness to vertical velocity and stability is significant but has little regional difference in both models. The coefficient in the relationship between cloudiness and relative humidity in the model needs to be adjusted and should be more conducive to the production of clouds.