Abstract: The gas-liquid two-phase flow refrigerant reaches the critical speed of sound after passing through the nozzle, forming an annular flow pattern with symmetrical distribution of the gas-liquid two phases, which can improve the uneven heat exchange caused by different pressures in each branch of the downstream heat exchanger.The critical flow injection process of the new rectifier nozzle liquid separator was simulated and studied by Fluent software.Using R507 re-frigerant, under the condition of constant nozzle throat diameter and different inlet pressures, the effects of nozzle constric-tion section, expansion section, throat length and outlet diameter changes on flow characteristics were simulated.The simu-lation results show that the injection velocity of the gas-liquid two-phase flow refrigerant increases with the increase of the inlet pressure within the inlet pressure range of 3.2 to 4.0 MPa, and the maximum velocity increases by 12.6%.When the inlet pressure is 3.6 MPa, the injection velocity of the two-phase flow refrigerant reaches the critical speed of sound.After the gas-liquid two-phase flow refrigerant is sprayed through four groups of nozzles with different structural sizes, the speed of the injection all reaches the critical sound velocity, and an annular flow pattern is formed in which the liquid phase surrounds the gas phase and is symmetrically distributed along the axis.The research can provide reference for the design of critical flow nozzle.