Abstract: To improve the accuracy, stability and real-time performance of the power system time transfer, a kind of high reliable power system timing method based on GNSS (Global Navigation Satellite System) is proposed. This method can support three control modes of the local rubidium clock: the Beijing local atomic time standard remote timing, GNSS system timing and the rubidium atomic clock frequency estimate correction, to ensure the electric system clocks in sync with the national time standard UTC(NIM), respectively when the time transfer standard or the transfer link is normal or faulted or a special period in which all means of communication are interrupted. Data comparison experiments are performed in the three timing modes. The results show that the standard deviation and the time stability in the three modes all meet and exceed the expected goal of synchronization with UTC (NIM).