Abstract: The ultimate capacity of a high steel falsework is investigated. According to the analysis of elastic buckling property of falsework with different design parameters and the spacing of vertical cross braces, it is found that the critical load and buckling model shape are very sensitive to the extension length of the vertical tube over horizontal tubes, the row spacing of vertical tubes, the lift height and the spacing of vertical cross braces. A reasonable measure in erection is proposed according to the effect of spacing of vertical braces and row spacing on the critical load. Considering the large deformation effect and material nonlinear property, the ultimate capacity analyses are taken and a formula for the calculated length of a vertical tube is given. Finally, According to the standard for checking and accepting of high falseworks, a formula for computing the ultimate capacity is proposed.