With the development of power electronic equipment in power, grid and load side, the systemic cascading failures across the voltage and region is increasing. The closed-loop control is needed. This requires Synchrophasor Measurement Units (PMUs) to measure phasors accurately and quickly. In this paper, a fast phasor measurement method for closed-loop control is proposed. The measurement error characteristic of traditional DFT under dynamic condition is revealed, and the influence of time mark position on accuracy and reporting latency is analyzed. The behavior of phasor measurement error and dynamic phasor model parameter with time mark at tail of window is analyzed. And the phasor modification method is proposed to reduce the reporting latency and ensure the accuracy. Simulation test verifies that the measurement accuracy and reporting latency is far exceed the standards of PMU for protection and control. It can be used for close-loop control. This work is supported by National Key Research and Development Program of China (No. 2017YFB0902901) and National Natural Science Foundation of China (No. 51627811, No. 51725702 and No. 51707064).