Abstract: Using the twodimensional symmetric incompressible laminar N-S equation, a numerical study of heat transfer characteristics of divergingconverging tubes with different generatrices is carried out with the finite volume method and SIMPLE algorithm. Three typical velocity and temperature profiles are specified at the inlet, i.e. uniform, linear and parabolic distributions. Effects of different inlet profiles and generatrices of divergingconverging tubes on heat transfer enhancement characteristics are studied. Variations of laminar and turbulent convective heat transfer characteristics in these tubes with different generatrices are obtained. Under the given conditions, a more appropriate generatrix is obtained through optimizing the heat transfer performance of the divergingconverging tube.