Abstract: The on-load tap changer（OLTC）is a critical device for regulating the output voltage of transformers, and it is also one of the most failure-prone components within it.Currently, the core-lifting detection method traditionally used for OLTC fault diagnosis is costly, time-consuming, and inflexible.This article introduces a simulation method for static contact defects in M-type oil-immersed composite OLTCs, exemplified by contact wear and erosion.The feasibility of this simulation method is verified through dynamic resistance waveform testing on actual OLTCs.This method is practical and has typical time-domain characteristics of dynamic resistance waveforms associated with specific defects, thus offering a valuable direction for the maintenance of OLTCs.