In order to analyze the failure and optimize the ductility of concrete-filled square steel tubular stub column with inner CFRP tube (CFSST-CFRP) under axial compressive load, the mechanical behaviors of specimens in related tests were analyzed by a finite element software ABAQUS. And failure analysis was made. A reasonable expression on ductility optimization and improvement is drawed through nonliner regression. The results indicate that CFRP fracture is a principal reason of CFSST-CFRP stub column failure under axial compressive load. Meanwhile, its ductility can be improved by increasing the value of ξf/ξs. Concrete-filled square steel tubular (CFST) stub column crack more seriously than CFSST-CFRP, and CFSST-CFRP stub column is not functioning adequately, without available CFRP bonded.