In view of the power loss problems caused by harmonic current, a comprehensive monitoring method of combining Fourier transform and wavelet transform is proposed to detect the harmonic current and analyze the power loss. The power system harmonic current is detected by the way of the wavelet multi-resolution analysis method; and the fundamental current is separated from the total harmonic current. The spectrum of low frequency harmonics in the steady-stage is obtained by Fourier transform analysis. The current distortion rate, power factor and line loss are calculated according to the amplitude of each harmonic to realize monitoring of harmonic current. The simulation results show current distortion rate and line loss will decrease with the decrease of low frequency harmonics amplitude; the line loss will increase with the increase of harmonic current content. The research results can provide a theoretical foundation for power quality monitoring and harmonic management in power system.