Abstract: According to the requirement of the International Satellite Cloud Climate Project (ISCCP), a cloud parameters retrieval algorithm is designed, which is fit to derive cloudiness over East Asia and the Tropical Ocean area. The satellite data is obtained from original S. VISSR of GMS-4, ranging from 50°N—30°S and 80°—175°E, and covering the midseason months—January, April, July and October of 1991.The total monthly mean cloudiness and hourly mean cloudiness are calculated with the method mentioned above. The results are examined by comparing with OLR climatological data in the periods. Furthermore, not only the seasonal variations in cloudiness, such as monsoon surge cloud system and the latitudinal movement of the ITCZ, but also seasonal distribution and the diurnal variability of cloudiness are studied in the region by using the results.