Nowadays, more and more attention is being paid to the new low Global Warming Potential ( GWP) refrigerant R1234ze (E). Mixing this refrigerant with R32 has been studied in recent years. We focused on contrasting the actual performance of the R1234ze(E)/R32 mixture (mass ratio: 27%/73%,named L-41b, with a GWP value of493) with R410A in a heat pump system. A test system of an air source heat pump was designed and built in an environmental chamber in order to compare the differences between L-41b and R410A under a wide range of working conditions. The compressor energy consumption ( COP),heating capacity, refrigeration cycle pressure ratio, and discharge temperature of the compressor were discussed and compared with R410A under similar working conditions. The results shows that, in the variable-condition experiments, the COP deviation decreased from 8. 6% to 2. 8% when the evaporation temperature increased from 5 ℃ to 13 ℃ at a constant condensation temperature of 38 ℃. The COP deviation was minimized when the condensation temperature increased from 30 ℃ to 42 ℃ at a constant evaporation temperature of 5 ℃ . The results further demonstrate that the L-41b mixture can be used to replace R410A in a heat pump system, particularly at relatively high cycle temperatures.