The invention discloses a state variable differential protection method for a power distribution network accessing to a distributed power supply with an aim to solve the technical problem about effective protection of the power distribution network with the distributed power supply connected therein. The state variable differential protection method includes that a line protection terminal judges state variable characteristics of a boundary switch of nodes connected with the line protection terminal, the state variable characteristics are shared with the line protection terminal of the boundary switch in the power distribution network via a communication network, boundary nodes are under the overcurrent state, fault location is in a protection area, and an action exit is protected. Compared with the prior art, the state variable differential protection method has the advantages that a power distribution network line is divided into a plurality of areas by the aid of a line switch, a section switch, a load switch and other switches, one of the area is taken as a protecting object, the fault in the area is judged by generated overcurrent fault sate and the fault location, the action exit is protected, and the power distribution network accessing to the distributed power supply is effectively protected.