The invention relates to a method for executing the phasor correcting for a synchronous phasor measuring apparatus, used for guaranteeing the accuracy of phasor calculating. In the method in the prior art, the hardware is adopted to measure the frequency and a method for adjusting a data window is adopted to guarantee the accuracy of the phasor measuring. In the method of the invention, a circuit positive sequence voltage is adopted to calculate the circuit frequency, after the offset deltaf of the system frequency relative to 50 Hz is calculated out, a least-squares method is adopted to fit the a series of amplitudes and angle error curve in 45 to 55 Hz, then the phasor is corrected by a look-up table. The method of the invention has fast computational speed, strong adaptability and high accuracy.