This paper proposes a novel ejector enhanced vapor injection cycle (EVIC) for air-source heat pumps. In the EVIC system, an ejector associated with an additional flash tank is introduced to enhance the overall system performance at low ambient temperature. The performances of the EVIC using R22, R290 and R32 are evaluated using the developed mathematical model, and then compared with those of the basic vapor injection cycle (BVIC). According to the simulation results, the EVIC with R22, R290 and R32 have 2.6-3.1%, 3.2-3.7% and 2.9-3.1% improvement in coefficient of performance (COP), 6.0-8.4%, 7.3-10.2% and 6.7-8.2% improvement in volumetric heating capacity compared with those of the BVIC under the same given operating conditions. Simultaneously, the EVIC also shows a good performance in reduction of the compressor discharge temperature at the given operating conditions. The performance characteristics of the EVIC may show its promise in heat pump applications. (C) 2015 Elsevier Ltd. All rights reserved.