The invention is a method of identifying and protecting differential protective difference current and differential protective transient TA abnormal state of a transformer. The differential abnormal alarming adopts ratio brake principle, the difference current abnormal alarming threshold value varies with the variation of load current of the transformer, when a phase difference current meets a condition, send out an abnormal alarming signal in no need of locking differential protection, the differential current initial value should be adjusted by avoiding the exciting current of the transformer, generally 0.03Ie, where Ie is rate current of the transformer, combine industrial frequency variation quantity voltage opening component and the current quantity, the distinguishing principle of differential protective loop transient TA breakage and short-circuit is allowable type, when differential protection starts and then meets conditions, consider it is a failure condition to open differential protection, and otherwise consider it is a start of differential protection caused by differential loop TA abnormality.