Abstract: The speed control system of the emergency diesel generator（EDG） in nuclear power plant is the core control component of the engine. In order to guarantee the stable operation and related safety function, the control to the speed and power input of the engine is very important. In this paper, taking the speed governor of the EDG sets in the nuclear power plant as an example, combing withe the typical fault cases, the function, control principle and operation mode are analyzed. A reasonable and feasible solution is put forward, which can provide reference for similar nuclear power projects and others.