To solve the location problems of discharging faults in oil-immersed power transformers, a novel location method based on metal in-oil analysis (MIA) is proposed. By the surface treatment for the internal components of high failure probability in the transformer, the potential failure sources in transformers are preset in the surface of these components and metal for position indication (MPI) is used for fault location. At the same time, through the integration with the existing partial discharge monitoring system and the online dissolved gases monitoring system, a relatively perfect fault diagnosis and location method for discharging faults could be achieved. The results show that the proposed method can increase the accuracy of fault location and lower the requirements in precision of the original certain fault location methods. The operation staff can also master more comprehensive latent fault information and be provided with new technical support for the realization of condition-based maintenance for transformers.