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In order to enhance the heat transfer performance of CO2 heat pump, based on the numerical simulation method of Fluent, the law of supercritical CO2 cooling and heat transfer characteristics and secondary flow in the horizontal elliptical tube whose torque is 100 mm or one infinity number under different mass flow are studied. In addition, concerning part coefficient of heat transfer and pressure drop brought by vertical elliptical tube, the influence of the length of the axial ratio b/a and the torque on the heat transfer performance is studied. Simulation results show that, the effect of buoyancy on the twisted elliptical tube is significantly larger than that of elliptical tube under low mass flow, and for the elliptical tube when supercritical CO2 is under the low mass flow G<200 kg/(m2·s2), the elliptical tube has a greater intensity of secondary flow caused by buoyancy, and the enhanced heat transfer is more pronounced; when supercritical CO2 is under the high mass flow G>200 kg/(m2·s2) , the twisted elliptical tube has a greater intensity of periodic secondary flow caused by self-structure, and the enhanced heat transfer is more pronounced; the heat transfer coefficient and pressure drop increase with the increasing degree of twist and flattening. It provides important theory and data support for the application of the twisted elliptical tube in CO2 heat pump.