For improving the synchronized phasor measuring accuracy of phasor measurement unit (PMU) in condition of power system dynamic transition, methods for improving PMU’s dynamic performance are researched. Phasor estimation model recommended in IEEE C37.118 which is based on Discrete Fourier Transformation (DFT) algorithm is used. Phasor measurement method based on DFT is improved and its characteristic is analyzed under out-of-band interference, oscillation, out-of-step, and short-circuit fault conditions. Equiripple filter is designed to process phasor data for ensuring synchronized phasor measuring accuracy. Finally, methods are realized in PMU and the test is carried out to verify the methods used. Synchrophasor measurement accuracy under dynamic processes is improved with the methods applied.