Abstract: Existing researches on the size effect of concrete filled steel tube (CFST) short columns mainly focus on members with circular section and ordinary strength materials, while the studies on size effect of high-strength concrete filled high-strength square steel tubular short columns are relatively limited. A multi-scale modeling method was proposed to study the size effect of the axial compressive behavior of high-strength concrete filled high-strength square steel tubular short columns. On the basis of verifying the multi-scale modeling method, a total of 24 multi-scale models were established. The influence of different parameters on the size effect of axial compressive behavior was analyzed. Furthermore, the calculation results of the axial compressive capacity formula of Professor Han Linhai, GB 50936−2014 code, AIJ 2008 code and T/CECS 987−2021 specification were compared with the simulation results. 4 size effect coefficient equations were proposed in order to effectively modify the 4 kinds of equations selected.