A method for identifying inrush current based on improve waveform asymmetry coefficient is disclosed. As a function of the differential current flow into the relay, The difference between fault current and inrush current waveform is compared. By subtracting the median value of waveform from the sampling value, the area surrounded by waveform is obtained by integration, which is divided by the areaof normalized quadrilateral to obtain a ratio independent of amplitude, initial phase angle and offset, and then the asymmetric coefficient of waveform is obtained by comparison with standard sine wave. Compared with the traditional second harmonic excitation inrush current identification, the invention can effectively identify the excitation inrush current, meanwhile, the principle has low requirements on the protection device and is easy to be computerized.