An air conditioning system and a method for controlling the same are provided. The air conditioning system includes an enhanced vapor injection compressor, first and second direction switching assemblies, first and second heat exchangers and a flash evaporator. The enhanced vapor injection compressor has a gaseous refrigerant discharge port, a gaseous refrigerant supplement port, first and second gaseous refrigerant suction ports, and a gaseous refrigerant return port. Pressure in a sliding vane chamber of a gaseous refrigerant cylinder corresponding to the second gaseous refrigerant suction port is equal to a discharge pressure at the gaseous refrigerant discharge port. A first pipe port of the first direction switching assembly is connected with the second gaseous refrigerant suction port, a second pipe port thereof is connected with the gaseous refrigerant discharge port and a third pipe port thereof is connected with the liquid accumulator, and the first pipe port is communicated with one of the second and third pipe ports.