Abstract: By use of a simplified stress-strain curve of steel fiber concrete and coefficient of section's coordinated strain, formulas for curvity ductility were derived. According to the curvity distribution of the column, the curvity distribution was assumed to be a broken line, then the length of the straight line and corresponding load and displacement can be calculated. The method of calculating theoretical load-deformation curve was presented. Comparison between testing results and calculating results indicated that the formulas for ductility coefficient and theoretical load-deformation curve are well verified.