In the DC traction power supply system, the locomotive starting current becomes bigger and bigger, locomotive starting process is more and more similar to the process of non-short circuit fault, multi locomotive starting process is closer and closer to the process of middle and far end short circuit fault, which lead to the increase of the possibility to make the DC feeder current rate and current increment (DDL) protection move mistakenly and refuse to move. This paper analyzes the existing DDL method and points out its shortage by simulation, and then puts forward a kind of protection method. This method is based on the current integral value, the ratio of the current average value and the maximum current value. It’s easy to distinguish non-metallic short-circuit fault current and the locomotive starting current, multi locomotive simultaneous starting current and the middle and far short circuit current, and the setting value is given. The reliability of this protection method is verified by simulation.