Abstract: Collapse accidents of super high formwork supports often happened in recent years. The main reason is the insufficient load-carrying capacity of the support. In this study, the initial imperfections for steel tubes are measured in some building sites and the statistical analysis of measured data is presented. Larger Initial curvature and insufficient thickness of tubers are taken into account and a new formula for ultimate capacity is proposed. In terms of Finite Element Method considering material nonlinearity and large deflections, the influence coefficients of initial curvature and thickness of tubes on ultimate capacity are given. Finally the influence of extension length of vertical tube over horizontal tubes on the critical load and the buckling mode are given, which can be the foundation of future research.