This paper considers cloud vertical structure,which is an important parameter affecting atmospheric radiation,and whose spatial and temporal distribution is a key component of global climate change.The occurrence of clouds over China and its surrounding areas(0-55°N,70-140°E)has been calculated based on the cloud layer products from CALIOP(the cloud-aerosol lidar with orthogonal polarization)at 1 km resolution.Cloud occurrence in different regions and seasons,and at different heights has been compared and analyzed.The results show significant regional differences in the frequency of cloud occurrence.Fewer clouds are found over the Mongolian Plateau and the northern Indian Peninsula,with more clouds appearing over the tropical seas and southern China.Cloud cover at night is slightly higher than during the day.Single-layer clouds are more common than multi-layer clouds in most areas,except the Mongolian Plateau and the northern Indian Peninsula.In most areas,high-level cloud accounts for the largest proportion of single-layer clouds;however,mid-level clouds are more common in southern China,and the northern parts of the western Pacific are often covered by low clouds.The occurrence of clouds in summer and autumn is generally greater than in spring and winter,especially over the northern Indian Peninsula,where clouds are most frequent in summer.Single-layer clouds over the Mongolian Plateau and the northern Indian Peninsula occur less frequently than multi-layer clouds,especially in winter.Furthermore,single-layer clouds are common over the eastern part of southwest China all year round.Over parts of the Tibetan Plateau in summer,high clouds account for the largest proportion(>35%)of annual single-layer clouds,as a result of topography and enhanced summer convection.