The traditional fast Fourier transform (FFT) method is prone to spectral leakage and fence effect under frequency variation and non-synchronized sampling conditions, which leads to a decrease in the accuracy of active power metering. For this reason, a new power metering method is researched, and a power metering method based on multiple second-order generalized integrator (MSOGI) is proposed. The MSOGI is used to extract the fundamental and each harmonic component and their quadrature components of single-phase voltage and current signals respectively, and realize the accurate measurement of active power based on separating the fundamental and harmonics. Meanwhile, a frequency adaptive module is introduced to improve the metering accuracy under frequency fluctuation. Simulation results show that the MSOGI-based power metering method can maintain high metering accuracy under different grid frequencies and harmonic conditions. The method innovatively combines MSOGI with instantaneous active power calculation, which provides a reliable solution for high-precision power metering in complex grid environments and can provide reference for subsequent related research.