With a constant-pressure mixing ejector, the performance characteristics of an ejector-expansion refrigeration cycle (EERC) using R1234yf as refrigerant have been investigated. Also, the performance of R1234yf and R134a in the EERC has been compared. The study shows that, at condensing temperature of 40 C and evaporation temperature of 5 C, the coefficient of performance (COP) and volumetric cooling capacity (VCC) of the R1234yf EERC peak up to 5.91 and 2590.76 kJ/m3, respectively. Compared with the standard refrigeration cycle the R1234yf EERC generally has a better performance, especially at the condition of higher condensing temperature and lower evaporation temperature. The COP and VCC improvements of the R1234yf EERC over the standard refrigeration cycle are also greater than that of the R134a cycle. In addition, the ejector design parameters including the pressure drop in suction nozzle, area ratio and component efficiencies on the R1234yf EERC performance have been analyzed.