Abstract: The present paper discusses the results of a numerical simulation about the performance of the single-phase convection heat transfer in converging-diverging tube.The mechanism of field synergy principle presented by Guo was conducted to reveal how to augmenting heat transfer when fluid is a fully developed turbulent flow.Some parameters are investigated on how to distribute along the stream-wise direction in the tube, such as the thermal boundary layer thickness, the turbulent intensity,the intersection angles between time-averaged velocity and time-averaged temperature gradient and the local Nusselt number.Numerical result reveals that the variations of T•cosθ are similar to the local Nusselt numbers along the stream-wise direction.The variation of the two parameters indicates that an enhanced cooperative interaction of velocity vector and temperature gradient vector will be created in the converging section, so a better field synergy is gained and heat transfer is augmented here.In the meantime, a worse field synergy is obtained in the diverging section.A comparison between two converging-diverging tubes is presented, which have different converging length while keeping the other geometrical parameters constant, such as rib pitch, rib height and tube diameter.Tube 1 with a longer converging length shows a better field synergy than Tube 2 with a shorter one.Hence heat transfer is enhanced when the converging length is longer.