Abstract: Based on the basic geological elements and events of petroleum system in Middle South of Xihu Trough, the abundance of organic matter of source rock in Middle South of Xihu Trough is medium to high, the kerogen type is Ⅲ humic.There develop bunches of various reservoir.The quality of reservoirs in petroliferous zone ranks to be Ⅱ to Ⅲ grade reservoir.The overlaid mudstone has good capacity for sealing.Pinghu and Sudi Structural Belt are promising as the petroleum occurrence, migration and entrapment are quite a match in time and space.