The invention relates to a method for estimating the residual magnetism of a transformer core based on the slope of a local hysteresis loop, which comprises the following steps: S1, measuring the saturation hysteresis loop of a transformer core material; S2, using a JA model to simulate the hysteresis characteristic of the transformer coil; S3, getting the relation between the residual magnetism and the slope of a local hysteresis loop near a residual magnetism point based on the JA model, and fitting the relation to get a corresponding formula relation; and S4, powering on and testing a transformer coil under test, getting the positive and negative slope near the residual magnetism point through electromagnetic relation conversion, and calculating the residual magnetism value according tothe formula obtained in the previous step. The method of the invention is simple. There is only the need to apply small positive and negative excitation and record the voltage and current in the residual magnetism calculation experiment. No complicated online experiment is needed. The test power is low, and the experimental cost is low.