Only through real-time and accurate detection of harmonic parameters can achieve the optimal configuration of harmonic compensation device and can achieve the goal of governing harmonics and inter-harmonics. As for the real-time and high-precision parameter estimation during the harmonics and inter-harmonics detection, this paper puts forward a high-precision correction method based on the fast detection of harmonics and inter-harmonics of 50% channel overlapped poly-phase filter structure. Meanwhile, it avoids the problem that detection capacity is reduced when harmonics and inter-harmonics are in overlapped channels. Theory analysis and simulation results show that the method can effectively improve the instantaneity of detection, still maintain a high accuracy, and is also easy to implement.