There are problems of complex structure and slow response of the ip-iq harmonic detection method based on instantaneous reactive power theory. Thus a harmonic current detection method based on an improved sinusoidal amplitude integrator is proposed. First, the method uses the output filtering characteristics of the second-order generalized integrator and the polarity selection characteristics of the sinusoidal amplitude integrator to construct a new integrator with stronger filtering performance and frequency and polarity selection. Then, the integrator is used to quickly and accurately extract the fundamental positive sequence component, and is also effectively applied to harmonic detection. When the grid voltage has DC bias problems, the phase-locked loop constructed by the integrator can also accurately lock the grid frequency and phase information. Finally, the theoretical analysis and simulation experimental results show that this method can extract the positive and negative sequence components of power grid voltage and load current without instantaneous symmetric component separation. The calculation is short and the harmonic detection is more accurate