The invention provides a device and method for controlling the rotating speed of an engine of an ISG type hybrid electric vehicle, and belongs to the technical field of power devices of hybrid electric vehicles. The device for controlling the rotating speed of the engine comprises an engine control unit, a rotating speed sensor and a hybrid electric vehicle control unit, wherein the rotating speed sensor is used for acquiring the rotating speed of the engine in real time and sending rotating speed signals of the engine to the engine control unit; the hybrid electric vehicle control unit is used for sending the target rotating speed to the engine control unit; the engine control unit is used for controlling a fuel spray nozzle of the engine to stop spraying fuel or not based on the target rotating speed and the acquired rotating speed of the engine. By the adoption of the device and method for controlling the rotating speed of the engine, the rotating speed of the engine of the ISG type hybrid electric vehicle can be effectively prevented from being too high.