Abstract: When input signal contains decaying DC component, full-wave Fourier algorithm based on periodic function will lead to larger error. To solve the problem, the paper proposed an improved algorithm based on full-wave Fourier algorithm. The algorithm need't increase sampling numbers, only need divide even or odd of sample sequence and makes Fourier calculation respectively, then accurate formula for each periodic component can be obtained. The simulation result showed that the algorithm has simple calculation and short data window, which can eliminate effect of decaying DC component effectively.