Abstract: Elastic-plastic constitutive model of circular steel tube, which is the stressed members of reticulated shell, is derived from mixed hardening considering cumulative damage. The discrimination criteria of instability and mechanical model after instability are introduced. VUMAT-DMB, the user material subroutine of ABAQUS suitable for 3D beam-column element, is compiled to apply cumulative damage model and instability of member in ABAQUS. The performance characteristics of the circular steel tube cantilever are compared with the results measured in the field to verify the theoretical analysis. The comparison indicates that VUMAT-DMB is accurate in evaluating the mechanical behavior of structure or members. The analysis results about a reticulated shell indicate that the cumulative damage has little effect on ultimate bearing capacity of structure, which decreased significantly when considering instability of member.