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In order to improve the measurement accuracy of synchronized phasor in the case of frequency offset, an adaptive DFT algorithm based on shifting window symmetrical was presented. First of all, sampling window length of DFT is determined by tracking the frequency of the power grid. Secondly, the composed phasor is calculated by utilizing three sampling windows which were away from a quarter sampling window length to each other. After compensating the fixed offset, the precise phasor measurement results can be computed. In addition, in order to quickly and accurately track the frequency, a zero-crossing algorithm based on three-phase signal for measuring frequency was proposed. The simulation results show that the proposed algorithm can meet the accuracy of synchronized phasor measurement, significantly decreases the computational complexity over the conventional method, and satisfies the requirements of real time applications for the smart grid. Keywords-adaptive DFT; variable length of window; synchronized phasor measurement; frequency measurement; shifting window symmetrical

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