Harmonic detection method based on Fast Fourier Transform (FFT) is widely used because the principle of FFT is simple as well as FFT can be easily embedded in measurement system. However, the detection accuracy is not high enough due to the issue of spectrum leakage and fence effect. Therefore, the improvement of harmonic detection method based on FFT has become an urgent problem to be resolved. Firstly, the harmonic detection method based on the theory of windows and the theory of spectrum line interpolation are introduced in this paper. The principles of the two improved methods are elaborated, and the research status of the improved methods is analyzed and summarized. Then the simulation are carried out to validated the feasibility of the two improved methods, and the corresponding conclusions are given respectively. Finally, the harmonic detection method based on the theory of windows and theory of spectrum line interpolation is summarized and the future researches are discussed. This work is supported by Project of the Key Subject of Hubei Education Department (No. D20181204), National Natural Science Foundation of China (No.51507091) and Master’s Degree Paper Foundation of China Three Gorges University (No. 2019SSPY052).