This paper analyzes the problems in short-circuit calculation model of DC traction system, and presents a set of fault calculation process meeting the requirements of protection setting and validation by analyzing different fault calculation models. The reasons for producing calculation errors are analyzed. The method of reducing the calculation error in steady-state short-circuit calculation is presented from two aspects of rectifier unit equivalent and knee current. The optimized calculation process is given. Based on the calculation model of transient current of DC-side output short-circuit and remote short-circuit, the overshoot theory is applied to come up with a new method to identify the output short-circuit, close-up short-circuit, and far end short-circuit, and method of calculating the transient current of close-up short-circuit is proposed. Simulation examples confirm the feasibility and accuracy of the proposed models and methods in meeting the requirements of protection setting and validation.