FFT Spectrum analysis can only dispose a limited number of discrete sampling signal, this is inevitable occurs the leak of time domain truncation, which decrease the accuracy of measurement. So we must use an approach to improve and increase the precision. The energy centrobaric method is adopted to satisfy the requirement of spectrum analysis precision in practical application. The simulation results show that, under the condition of a whole cycle sampling, the accuracy has been improved greatly and is sufficient to meet the requirements of practical application.