The present invention discloses a method of identifying a tail current based on current derivative and differential current zero-crossing. The method is characterized in that with the help of the differential filter, N-point differential treatment is carried out on an original current waveform to filter a DC component in the original current waveform, eliminate the migration of the waveform to a time shaft and reduce the unfavorable influence of the waveform migration on the half-wave integral; within a 1/2 cycle, an absolute value of a current waveform derivative before difference is calculated continuously, whether a differential current waveform exits the zero-crossing is determined, and the amplitude of the differential current waveform is calculated via a half-wave integral method; within the 1/2 cycle, if the differential current waveform zero-crossing is not identified, the absolute value of the original current waveform derivative is reduced continuously, and the amplitude calculated via the half-wave integral method is less than a set threshold value, a current is determined as the tail current, and the differential protection, the overcurrent protection and the failure protection are locked immediately, thereby improving the action reliability, preventing the maloperation, and having the good application prospect.