As can be seen from research efforts in the literature, although R32 has been studied experimentally and theoretically, all works have been conducted on a conventional single-stage vapor compression cycle. Figure 1 shows the schematic of a flash tank vapor injection two-stage cycle. Compared to a conventional single-stage cycle, a flash tank vapor injection cycle has two-stage expansion. The liquid and vapor is separated in the flash tank after the first stage expansion. The vapor is injected to the compressor, and the liquid refrigerant go through the second expansion valve, and then flows through the evaporator. It’s known from the literature that vapor injection system has benefits of potential capacity and COP improvement, especially at low temperature heating condition (Xu et al.,2011). As there was no open publication on such research effort, employing refrigerant R32 in a vapor injection two-stage system is worth for investigation. This paper focuses on comparing the performance between R410A and R32 in a flash tank vapor injection system at different operating conditions.