Abstract: The SST k-ω turbulence model was used to numerically simulate the heat transfer characteristics of supercritical pressure CO₂（S-CO₂）in constant-section circular tube,horizontal diverging tube and diverging tubes with different inclination angles under cooling conditions.The computational results indicate that compared with that of the uniform cross-section tube,the total heat transfer coefficient of the horizontal diverging tube and the 30°inclined diverging tube are increased by 32.33%and 33.12%respectively under same heat transfer area,and the pressure drop are decreased by 53.87%and 9.86%,respectively.Using comprehensive Performance Evaluation Criteria（PEC）,it is found that the comprehensive performance of the horizontal diverging tube is the best.Based on the assumption that S-CO₂has“phase-transition-like”at pseudo-critical temperature T_pc,the distribution of the liquid-like film along the length of the tube is obtained,and it is found that at the same section,the thickness of the liquid-like film of the 30°diverging tube is the smallest,the liquid-like film thickness of the constant-section circular tube is the biggest.The mechanism of heat transfer enhancement is explained from the point of view of supercritical two-phase-like.