To solve the problem of harmonic detection in power quality analysis, Variational Mode Decomposition (VMD) is applied to harmonic detection in power system. The method uses the band division capability of VMD to separate the harmonic modes effectively. The decomposition number of VMD is determined by spectrum analysis of harmonic signal. And harmonic modes characteristic parameters such as amplitude and frequency are extracted by Hilbert transform. A method for disturbance location based on singular value decomposition is proposed, which locates the start-end time and amplitude-varying time of transient harmonic accurately. Simulation experiments of different harmonic signals verify the efficiency of the proposed method, indicating that it both has high detection accuracy under the conditions of non-noise and low Signal Noise Ratio (SNR), and has good noise robustness. This work is supported by National Natural Science Foundation of China (No. 51277134).