Abstract: The effects of different t8/5 on microstructure and mechanical properties of heat-affected zone(HAZ) of high-strength residual heat treatment steel bar were studied by using Gleeble-3500 welding thermal simulation tester. The results show that, with the increase of t8/5, the microstructure of coarse grain heat-affected zone (CGHAZ) changed from feather-like upper bainite, strip-like lower bainite and ferrite to granular bainite, pearlite and ferrite. The impact energy of heat-affected zone at room temperature increased firstly then decreased and reached the maximum when t8/5=100 s. When t8/5was more than 60 s, the microstructure of CGHAZ was made of ferrite and pearlite. The micro-hardness of heat-affected zone decreased with the increase of t8/5. The high-strength residual heat treatment steel bar would be meet the production needs with the range of t8/5 from 20 s to 300 s.