Abstract: It is necessary to study the residual stresses and thermo-harm of the direct welding joint of steel tubular members for researching the calculation of ultimate strength and fatigue life.According to the thermo-effect of welding process of tubular K-joint, the description of temperature field for welding process during heating and cooling, the mathematical model of heat transfer and phy sical model suitable to practical production, the coupling-calculation of temperature field and welding stress filed has been taken.The thermo- physical performance parameters and mechanical property parameters as the nonlinear functions of temperature were taken into consideration. The distributions of residual stresses and residual strains were in agreement with the experimental failure pattern of tubular Kjoint. For the local buckling failure of brace tube in tubular K-joint experiment, the concept and principle of welding thermo-harm is presented.