An enhanced vapor injection air conditioning system is provided and includes: a vapor injection compressor, a direction switching assembly, a first outdoor heat exchanger, a second outdoor heat exchanger including first and second heat-exchange flow passages, and an auxiliary electronic expansion valve assembly. A main electronic expansion valve assembly is connected between a first end of the first heat-exchange flow passage and a second end of the first outdoor heat exchanger. The auxiliary electronic expansion valve assembly has a first end connected with an inlet of the second heat-exchange flow passage, and a second end connected to a second end of the first heat-exchange flow passage or between the main electronic expansion valve assembly and the first heat-exchange flow passage. A ratio DB of a sum of a caliber of the main electronic expansion valve assembly to that of the auxiliary electronic expansion valve assembly has a range of 1≤DB≤7.