Abstract: Using long time hourly 0.1°×0.1°resolution merged precipitation products provided by the National Meteorological Information Center of China Meteorological Administration and the NCEP reanalysis data, the characteristics and the causes of summer precipitation in Liaoning province have been analyzed. The results are summarized as follows. (1) The greater averaged daily precipitation frequency in Liaoning province locates in the east, which is closely related to the fact that this area locates in the Qianshan-Longgang mountain region where the southerly wind prevails in middle and low level in summer.(2) The greater average hourly rain rate in Liaoning province also locates in the east. There have two main reasons. Firstly, this area locates in the moist tongue in the middle and low level specific humidity fields. Second, there has a center of ascending velocity there in middle and low levels caused by the southwesterly wind uprising forced by its meeting with Qianshan-Longgang mountain.(3) The diurnal variation characteristics of precipitation in Liaoning province is evident. The diurnal rain peak occurs most frequently from afternoon to midnight in mountain areas and in the northwest, and occurs most frequently in the early morning hours in the central plain and the southern coastal area of Liaoning province.(4) When the synoptic system is at its preliminary stage or at its later stage, the diurnal variation occurs as mentioned above. But, when the synoptic system moves or develops, the local diurnal rain peak often occurs at that moment.(5) The diurnal precipitation variation characteristics seems to be independent of the synoptic type, i.e., it exists in all kinds of rain cases.(6) The local thermodynamic and dynamic cycle, the strengthen nocturnal southwest warm and wet air stream from the sea caused by the individual topography, i.e., mountains and plateaus in the west, plains in the middle, mountains and hills in the east and sea neighbored the south, are the main factors affecting the diurnal rain variation in Liaoning province.