A transformer secondary side load matching device belongs to the technical field of transformers. The invention aims to perform resistor matching of secondary side circuits of transformers with different transformation ratios, so that the transformer secondary side load matching device which can conveniently observe a transformer current value wave curve and an automatic matching method can be obtained. The device is composed of a power conversion part, a sensor collection part and a resistor matching part. Under a precondition of lots of experiment data, the invention provides a method of performing determination, calculation, matching and automatic load accessing according to voltage values at two sides of a transformer by employing the modern computer technology and taking the host computer program of a transformer on-load tap-changer performance characteristic alternating current test device as the base, so that when the transformer performs on-load tap-changer motions, output current of a secondary side is adjusted to be controlled within a certain measuring range, the amplitude of change in current is reduced, a test waveform which is uniformly stable, smooth and obvious can be obtained during the test of transformers with different transformation ratios, the adaptability of a whole set of alternating current test device in the reality is improved, and the whole set of alternating current test device is enabled to accurately perform related tests and analyze results.