A harmonic detection method based on a combination of continuous wavelet transform and discrete wavelet transform is proposed. Firstly, harmonic frequencies are detected by the magnitude of CWT coefficients with a determined scale range and step size, while need not determine the harmonic decomposition level according to the harmonic numbers in advance. And then the DWT method is used to detect harmonic amplitude according to identified harmonic components. Simulation results are completed by Matlab, which show the proposed method can solve the problem that a undetermined decomposition level according to unknown harmonic numbers effectively and can detect the harmonic frequencies and the corresponding amplitudes accurately and reliably. Therefore, this proposed method is a valid method to harmonic detection in power system.