In order to effectively detect load-current signal in power grid, a harmonic current combination detection method based on sliding-window iterative DFT and wavelet packet analysis is proposed, this method firstly uses sliding-window iterative DFT to separate the fundamental component and harmonic component in load-current signal, then uses wavelet packet to analyze the obtained harmonic component, so as to more accurately separate the residual fundamental wave and every harmonic content, and then uses MATLAB to conduct simulation experiment. The experiment results prove the validity and accuracy of the proposed method.