Abstract:.Time synchronization technology is one of the key technologies of smart grid operation.In order to solve the problems of low reliability and unstable time service performance caused by traditional satellite timing in smart grid, this paper first establishes a ionospheric free combined BDS3timing algorithm based on sequential least squares . At the same time, two errors , the multi frequency observation noise and the "day-boundary jump" of the carrier phase, are identified in the algorithm. For these two errors, the correction models of the "day-boundary jump" elimination algorithm based on the invariable a priori ambiguity and the pseudo range measurement noise correction algorithm based on altitude angle classification are established respectively. The experimental test and analysis show that the ionospheric free combined BDS3 timing algorithm based on sequential least squares proposed in this paper, compared with the classic satellite timing method, has significantly improved about 15%。