Voltage fluctuation and flicker is an important norm of power quality.With large numbers of interharmonics injected into the grid，the interharmonics-caused flicker is attracting ever-increasing attention of researchers.Calculation of interharmonics-caused flicker depends on the accurate detection of interharmonics，but the interference between harmonics and interharmonics，and that between two interharmonics seriously affect the accuracy of interharmonics detection.To solve this problem，this paper proposes a frequency-searching method by combining with quasi-synchronization in the time-domain and windows and interpolating fast Fourier transform（FFT）.This method yields the matching level between the theoretical spectrum and the actual spectrum of multiple interharmonics，by analyzing the windowed interharmonics spectrum.Then interharmonics are detected by searching for the frequencies corresponding to the maximum matching level.The simulation results indicate that this method effectively reduces the impact of the harmonic leakage and the main lobe width effect of adjacent windowed interharmonics while accurately calculating the interharmonics-caused flicker.