Accurate transformer models are crucial for the electromagnetic transient analysis of transformers, while most transformer models require a multitude of parameters. In this paper, a 500kV auto-transformer model considering the capacitive effects is built, and the corresponding parameters determination method is presented. In the parameter determination method, only the factory test report of the transformer is needed. The open-circuit and short-circuit simulations are carried out. The results show that the maximum error between the simulation and corresponding test presented in the factory test report is 2.82%, indicating that the auto-transformer model and parameter determination method are accurate. The proposed transformer model and parameter determination method are useful in engineering applications.