Abstract: An experimental study is conducted to investigate the longitude residual stress in Q800 high strength steel welded I-sections using the sectioning method. The effect of the width-thickness ratio of web and flange on the distribution of the residual stress, including the interaction and stress equilibrium, was analyzed. And the models of estimating the distribution and magnitude of residual stress are proposed. The results show that the distribution of the residual stress of Q800 high strength steel I-shaped cross-section is similar to that of ordinary-strength steel. The tensile stress which locates around the welding zones and the edges of flange presents an irregular relation with the changes of width-thickness ratio of plates. The constant compressive stress distributes in the middle portion of the projecting flange and web, and decreases as the width-thickness ratio of plates increases. The remaining parts are the transition regions from tensile stress to compressive stress. The residual stress in the flange and web can satisfy the self-equilibrium condition, and no interaction between the flange and web exists.