In order to further improve the calculation accuracy of the windowed interpolation algorithm, this paper proposes a new five terms cosine window function, four order Hanning self-multiplication window function, based on this window function and three spectral lines interpolation correction formula, the general amplitude, phase and frequency interpolation correction formula are derived; using these general interpolation formula, we can extract the fundamental and harmonic’s amplitude, phase and frequency parameters in the measured voltage and current signal, and then we can calculate the fundamental and harmonic electric energy accurately. The simulation results show that, because of the window function has better main lobe and side lobe performance, which can effectively suppress the influence of spectrum leakage and fence effect, so based on this window function, the new algorithm for computing electric energy has higher accuracy.