Based on the determined stress-strain relationship of steel and concrete after fire, a temperature field and mechanical model of bar-reinforced concrete-filled square steel tubular columns after fire was set up with using ABAQUS, and the model has been validated by testing results. Then this paper analyzed the side of section, bar ratio, fire duration time, steel ratio and material strength parameters on the bearing capacity of bar-reinforced concrete-filled square steel tubular columns after fire. It is found that fire duration time and side of section is the dominant factor. Lastly this paper puts forward a theoretical formula of bearing capacity of bar-reinforced concrete-filled square steel tubular columns after fire, for the post-disaster restoration and provides references for the reinforcement.