In this study, high temperature tensile properties of high strength steels(POSTEN60, POSTEN80) were investigated. The three-dimensional thermal elastic-plastic analyses were conducted to investigate the characteristics of welding residual stresses in welds of high strength steels on the basis of thermal and mechanical properites at high temperature obtained from the experiment. According to the results, high temperature tensile strength of POSTEN60 steel deteriorated slowly to 10$0^{circ}C$. As the temperature went up, the tensile strength became better because of blue shortness, and it deteriorated radically after reaching to the maximum value around 30$0^{circ}C$. For the POSTEN80 steel, high temperature tensile strength deteriorated slowly to 20$0^{circ}C$. As the temperature went up the tensile strength became better and it deteriorated slowly to $600^{circ}C$ after reached to the maximum value around 30$0^{circ}C$. Strain of high strength steels at the elevated temperature increased radically after the mercury rose to $600^{circ}C$. The strain hardening ratio of POSTEN60 steel was larger then that of POSTEN80 steel at the elevated temperature as in the case at the room temperature and it became smaller radically after the mercury rose to 40$0^{circ}C$. And, in the welding of high strength steels, increasing tensile strength of the steel (POSTEN60<POSTEN80) increased residual stress in welds.