A method for controlling a vehicle cooling system is provided. The system includes an engine, an EGR cooler, an oil cooler, a heater, a radiator, and a controller. The engine, the EGR cooler, the oil cooler, the heater, and the radiator are respectively connected through a coolant line and coolant circulates through the engine, the EGR cooler, the oil cooler, the heater, and the radiator by operation of a water pump. The controller receives the coolant from the engine and operates a control valve that is connected with the oil cooler, the heater, and the radiator. The method includes sensing driving conditions and operating the control valve when a warm mode is required to increase the temperature within the vehicle based on the sensed driving conditions. The control valve is operated based on first to third modes depending on a coolant temperature.