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Obtaining correct fundamental phasor of power systems is of great significance to the intelligent dispatching of Smart Grid. Considering that fundamental frequency of grid is likely to fluctuate and harmonics may exist, some commonly used algorithms are hardly to satisfy measuring requirement. This paper proposes a novel synchronized phasor measurement algorithm based on time-frequency transform (TFT). As the transform kernel of TFT, time-frequency atom (TFA) has compact distribution characteristic in time-frequency domain. More importantly, the radius of time or frequency domain window of TFA can be adjusted using scale factor, and is independent with central frequency. Thus, measurement accuracy and dynamic characteristics of the TFT based phasor measurement algorithm can be well achieved. MATLAB simulation results indicate that TFT has better dynamic characteristics than wavelet transform, and it can obtain fundamental phasor of voltage and current accurately without synchronous sampling, overcoming the interference of harmonics and noise. Additionally, other electrical parameters such as power can also be estimated using the output of TFT. Finally, to further verify the effectiveness of the proposed algorithm, test results based on digital signal processor (DSP) are also presented.