The invention discloses an engine cooling system and a temperature control method of cooling liquid thereof. The engine cooling system comprises a heat radiator, a water pump, a circulating water jacket, an electronic thermostat, a cooling fan, a cooling liquid temperature sensor and an engine control unit, wherein the control unit determines the cooling liquid target temperature of an engine under the current operation working condition according to acquired signals, such as engine rotating speed, load, speed, air inlet temperature, and the like and ensures that the engine works under the optimal cooling liquid temperature condition by controlling the heating time of the electronic thermostat and the high and low speed running of the cooling fan.