NOVELTY - Temperature of a fuel cell system is controlled by receiving, at a controller, a coolant outlet temperature from a water temperature sensor in a state where a reference temperature for each stage is determined with respect to the coolant outlet temperature and a target rotational speed for each stage is determined based on the coolant outlet temperature. A proportional integral control is performed by the controller with respect to each rotational speed of a coolant pump and a cooling fan at target rotational speed for each stage determined based on detected current coolant outlet temperature.    USE - Method of controlling temperature of a fuel cell system used in vehicles. Uses include but are not limited to sports utility vehicles (SUV), buses, trucks, commercial vehicles, boats, ships, aircraft, hybrid vehicles, electric vehicles, or hydrogen-powered vehicles.    ADVANTAGE - The method can control the coolant pump and the cooling fan in the fuel cell system to reduce power consumption of the coolant pump and the cooling fan by optimizing their operations, prevent the occurrence of flooding and dry-out, and improve the performance of the fuel cell system and water removal efficiency.    DETAILED DESCRIPTION - Control of temperature of a fuel cell system comprises receiving, at a controller, a coolant outlet temperature from a water temperature sensor in a state where a reference temperature for each stage is determined with respect to coolant outlet temperature and a target rotational speed for each stage is determined based on coolant outlet temperature. A proportional integral control is performed by the controller with respect to each rotational speed of a coolant pump and a cooling fan at target rotational speed for each stage determined based on current coolant outlet temperature detected by water temperature sensor. An INDEPENDENT CLAIM is included for a system for controlling temperature of a fuel cell system, comprising a sensor for detecting a temperature at a coolant outlet of the fuel cell system and sending to the detected temperature to a controller. The controller receives a coolant outlet temperature from the sensor, where a reference temperature a stage is determined with respect to the coolant outlet temperature and a target rotational speed the stage is determined based on the coolant outlet temperature, and performs proportional integral control with respect to each rotational speed of a coolant pump and a cooling fan at the target rotational speed.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic diagram showing of a system for controlling the temperature of a fuel cell system.