The dynamic performance requirement for PMU becomes a hotspot in recently years. The paper discusses DFT correction algorithm based on frequency difference which is used widely by the popular manufactory. It is obvious that DFT correction algorithm is very adaptive under power system steady condition with high accuracy. While under dynamic condition such as low-frequency oscillations, fault, out of step and so on, DFT correction algorithm is not capable. The paper presents a new algorithm to improve measurement accuracy under dynamic condition by adding FIR to DFT factors, which can also be used under power system steady condition, and also gives its concrete realization process. At last, the latest test specification and method of dynamic performance for PMU are introduced.