To effectively detect jump phase, start and end time and sag amplitude of voltage sag, a method based on complex wavelet transform and teager energy operator is proposed in this paper to detect these three characteristics. The construction principle of complex wavelet and its application to the detection of voltage sag with teager energy operator are studied in detail. For the voltage sag signal with noise, the teager energy operator is used to detect the sag amplitude of the approximate signal obtained by the db4 real wavelet transform, and the db4 complex wavelet transform is used to detect the phase of two approximate signals before and after the sag, then the start and end time and jump phase will be given from the difference of two phases. The anti-interference and real-time performance of the algorithm is verified by matlab simulation results.