The purpose of this paper is to investigate the heat transfer performance of the tubes with twisted elements at different twist ratio variation Tv. On the constant wall temperature boundary condition

the characteristics of heat transfer and pressure drop are investigated experimentally and numerically. Tv are within the scope of -5-5 and water is used as working fluid．The comprehensive heat transfer and heat enhancement mechanism are analyzed at different Tv. The results show that the condition of Tv>0 along the flow direction is superior to the condition of Tv=0. The average heat transfer enhancement ratio of Tv=2.5 is 5.0% higher than that of Tv=0. However，the heat transfer effect of Tv<0 is inferior to Tv=0

and thus the layout should be avoided. The flow field structures are altered by the change of the twist ratio of the elements. For the case of Tv>0

the vorticity and the action range of the detour-flow vortex within more than half of the element area are improved significantly with the increase of Tv. At the same time the coordination of pressure

velocity and temperature fields is improved and heat transfer is enhanced accordingly.