Due to the inherent hysteresis characteristics of ferromagnetic materials, remanence will be generated in the transformer core after various tests and excision operations. This article studies the influence of remanence on on-site tests of transformers through theoretical analysis and on-site test verification. The research results indicate that: remanence can cause the test results of transformer low voltage no-load current to be larger; remanence can cause the test results of transformer voltage ratio to be larger; the sweep frequency range of transformer winding frequency response test is 1 kHz ~ 1 MHz, and remanence can affect the starting section of the winding frequency response curve; if the sweep frequency range is extended to 20 Hz ~ 1 MHz, remanence will cause the resonance point frequency of the winding frequency response curve in the range of 20 Hz ~ 1 kHz to increase; remanence has a relatively small effect on the low voltage short-circuit impedance test of transformers; remanence will cause the resonance frequency of transformer partial discharge test to be high, which may exceed the normal operating frequency range of frequency conversion power.