Based on conventional high-altitude aerial and ground data,regional intensive rainfall data,Doppler weather radar and satellite cloud data,the occurrence and development process of a regional rainstorm in South Shaanxi during July 17- 18,2010 was discussed deeply.The results showed that the occurrence and development of the mesoscale weather system resulted in the heavy storm directly besides favorable large-scale background,and the the occurrence and development of the system had strong local and sudden characters.In addition,heavily concentrated water vapor in the troposphere at low and middle altitudes as well as existence of unstable conditions of convection might be favorable to the development of the system,while dynamic action of terrain,ground weak cold front and disturbance of the low-level jet stream might trigger the occurrence and development of the system.