Through the particle image velocimeter (PIV) flow field experiment combined with heat transfer experiments, the effects of structural parameters such as spiral pitch, wire diameter and median diameter ratio of insert-spiral vertical upstream tube on the flow field and heat transfer performance were studied under different Reynolds number. The results showed that the insert-spiral can effectively disturb and mix the fluid in the tube, and a number of longitudinal vortexes were formed in the tube, and the vorticity of liquid increased near the wall of the tube, which was beneficial to the enhancement of heat transfer. When the Re number was the same, the average flow velocity v, Nu number and the comprehensive heat exchange performance (PEC) in the tube increased with the increase of the wire diameter, and increased with the decrease of the median diameter ratio. As the pitch increased, all three parameters tended to increase, and began to decrease when the pitch was greater than 20 mm. The resistance coefficient f of the fluid in the tube decreased with the increase of the wire diameter and the pitch, and increased with the increase of the median diameter ratio. In general, when the Re number was lower, the comprehensive heat transfer effect was best with a pitch of p=20 mm, a wire diameter of e=1.6 mm, and a median diameter ratio of D/d=0.75.