Abstract: Using NCC/IAP T63 atmosphere-ocean coupled model, a 20 years'integration was processed, and its capability to simulating cloud and radiation was also analyzed in detail. The results show that the model can simulate the basic distribution of cloud cover, however obvious differences still exist compared to ISCCP satellite data and ERA reanalysis data. The simulated cloud cover is less in general, especially the abnormal low values in some regions of ocean. By improving the cloud cover scheme, simulated cloud cover in eastern ocean, summer hemisphere's ocean from subtropical to mid-latitude is considerably improved. But in tropical Indian Ocean and west Pacific the cloud cover difference is still evident, which is mainly caused by the deficiency of high cloud simulation in these regions caused by deep cumulus convection. In terms of the analysis to radiation and cloud radiative forcing, it was found that simulation on long wave radiation is better than short wave. The simulation error of short wave radiation is caused mostly by the simulation difference in short wave radiative forcing, sea ice and snow cover, and also by not involving aerosol's effect. The simulation error of long wave radiation is mainly resulted from deficiency in simulating cloud cover and underlying surface temperature. Corresponding to improvement of cloud cover, simulated radiation(especially short wave radiation) in eastern ocean, summer hemisphere's ocean from subtropical to midlatitude is remarkably improved. This also brings obvious improvement to net radiation in these regions.