The ultimate load-bearing capacities of axially-loaded steel tube composite column filled with steel reinforced concrete under three-dimensional stress based on the unified strength theory are analyzed in this paper. The influence of thickness-length ratio and scale effect are considered by introducing the reduction factor of equivalent constraints and concrete strength reduction factor, respectively. The nonlinear three-dimensional finite element analysis of the steel tube composite column filled with steel reinforced concrete is performed by the finite element software ANSYS. The numerical and the analytical results are compared with experimental results and good agreement can be observed. A series of numerical simulation technologies is studied and described in detail, such as selecting element type, defining material model of steel and concrete, establishing global finite element model with discrete reinforced bars elements, applying loads to the specimens, and setting solution controls option. The results indicate that ANSYS finite element software may well simulate the behavior of the steel tube composite column filled with steel reinforced concrete under axial compression through reasonably selecting parameters.