In order to locate the low frequency oscillation source quickly and take appropriate measures to suppress the oscillation, a locating method of low frequency oscillation source based on the power network topology is proposed. Energy production characteristics of the region of oscillation source under the local oscillation mode and inter-area oscillation mode are analyzed. Then, based on graph theory and cut-set oscillation energy, the concept of the cut-set of maximum oscillation energy flow is put forward. The oscillation source location is transformed into the search of the cut-set of maximum oscillation energy flow. According to the transmission characteristics of the oscillation energy flow, using K shortest paths to limit the search scope, and using travel replacing algorithm to find all cut-sets, then the oscillation source is limited to the inside of the cut-set of maximum oscillation energy flow. The West Inner Mongolia Power Grid is used to verify the correctness of the locating method, and the method is applicable to both local and inter-area oscillation mode. Therefore, this method has some practical value.