The invention relates to a relay protection method in the field of electrical system. It discloses a method for computing negative direction by the testing negative voltage and negative current at safety arrangement, then using negative direction unit to lock zero-point direction unit. It has the following steps: computing the value of negative voltage and negative current at safety arrangement after wire protection device sampling and filtering current and voltage waveform of mutual inducer, quoting negative direction when its direction of zero-point is headway, if it is negative direction, locking zero-point protection unit, while if it is non-negative direction (including headway and direction unit doesn't move), then allowing zero-point direction unit to trip though protecting exportation.