Abstract: An improvement of the fast Fourier transform (FFT) algorithm was presented, which uses the fast attenuation characteristic of Fourier transform. This algorithm can effectively eliminate leakage component spectrum, realize non-rounded harmonic precision testing and overcome the shortcomings of the traditional FFT, only by a simple transformation of FFT. Because this algorithm is more similar to but simpler than the form FFT in algorithm structure, it is more suitable for storage on microprocessors which are limited-resource. A harmonic detection device based on digital signal processing (DSP) was designed to prove that the algorithm is applied to the convenience of microprocessors.