A cooling system for a vehicle includes: an engine cooling circuit circulating a coolant to an engine mounted in the vehicle; an electronics cooling circuit circulating the coolant to an electrical equipment and a motor mounted in the vehicle; a reservoir tank connected to the engine and the motor and respectively compensating the coolant to the engine cooling circuit and the electronics cooling circuit; and a control valve connected to a first connection pipe connected to the reservoir tank and selectively connected to the engine cooling circuit and the electronics cooling circuit depending on a temperature change of the coolant during a cold driving mode or a warm driving mode of the vehicle to control a flow of the coolant.