The invention relates to an optimal configuration method for a synchronous phasor measurement unit, which comprises the steps of acquiring an impact load to be monitored; establishing a geographic wiring diagram network structure topology by taking substations as nodes and taking power transmission lines of different voltage levels as branches; determining a connection matrix of each node in the network according to the geographic wiring diagram network structure topology; acquiring an array of upper-level substations directly connected with a substation corresponding to the impact load to bemonitored according to the connection matrix, wherein elements of the array comprise a substation serial number, the number of lower-level impact loads of the substation and state parameters of the synchronous phasor measurement unit; and determining nodes requiring configuration of the synchronous phasor measurement unit according to the array. The invention further provides an optimal configuration system for the synchronous phasor measurement unit. According to the optimal configuration method and system for the synchronous phasor measurement unit, the number of the synchronous phasor measurement units required to be configured can be reduced to be maximum extent while realizing accurate positioning and monitoring for a load-side compulsive oscillation and disturbance source in an electric power system.