The invention discloses a method for distinguishing a transformer magnetizing rush current based on weight mathematical morphology. The method comprises the following steps: (1) collecting a difference current signal of current transformers on two sides of a transformer differential protection according to a certain sample frequency, (2) judging whether a break variable among a plurality of continuous sampling values is larger a preset break variable limit value, if yes, collecting data of a half circle in a delayed mode and carrying out a step (3), or, continuing sampling, (3) selecting a data widow as a difference current signal value with the length of a half fundamental frequency, carrying out processing on the weight mathematical morphology and obtaining a processed signal waveform, and (4) obtaining a wave-shaped correlation coefficient, judging whether the wave-shaped correlation coefficient is smaller than a preset setting value of the wave-shaped correlation coefficient, if yes, judging that the interior of a transformer breaks, or, distinguishing the transformer magnetizing rush current. The method has the advantages of being simple in steps, small in calculated quantity, short in delayed time, easy to implement, strong in generality and the like.