The distribution statistics of cloud layers over China Sea and adjacent sea area are derived from 4-year CALIPSO 5 km level 2 version 3 lidar cloud layer data from 2007 to 2010. The changes of cloud occurrence frequencies by year, month and geographic location are analyzed. The statistics of cloud occurrence frequency from 2007 to 2008 MODIS data are used for the comparison. The results show that, in the research area, the differences of cloud occurrence frequencies are less than 3% for clouds with same number of layers in different years, and the regional distributions of cloud occurrence frequencies of different years are similar. Cloud occurrence frequencies are higher than 80% near the equator and less than 50% close to 20
N. The statistical results are consistent with MODIS data. Cloud occurrence frequency has obvious differences for different months within the same year and the maximums of 4 years are all in June or July respectively. The changes of cloud occurrence frequency with latitude are obviously for the clouds with same layer number within the same year.