The invention relates to a transformer substation bus differential protection method and device, and belongs to the technical field of power system relay protection, and the method comprises the steps: collecting differential current, and judging whether differential protection starting discrimination is met or not; if differential protection starting judgment is met, judging whether each phase ofdifferential protection to be an internal fault or not is judged according to the A phase, the B phase and the C phase; and when a certain phase differential protection is judged to be an internal fault and the number N0 of action equations in continuous N1 sampling points is greater than or equal to n1, judging that the phase differential protection relay acts, and after the phase differential protection relay acts, the differential protection acts instantaneously. According to the invention, by improving the discrimination logic of the action of the differential protection relay, the discrimination accuracy of the action of the differential protection relay is ensured, and the problem of differential protection maloperation caused by misjudgment of the action of a certain phase of differential protection relay is avoided.