It is important to realize real time measurement of the bus voltage phasor of substations and the power angles of generators at different locations for stability control. Traditionally, EMS uses the data of bus voltages, line currents and phase angle between them to calculate the power angles of generators. This is an indirect method. The calculation time of the method is too long to be used in real-time control. A new method based on GPS is proposed in the paper which can not only measure the bus voltages and currents phasor of substations, generators at different locations, but also the power angles of generators in operation. The principle and realization are discussed in the paper. Theoretical analysis and experimental results prove that the new measurement method is correct and effective.