Setting transmission member in concrete-filled rectangular steel tube (CFRST) column has solved the problem that steel tube and concrete is difficult to work together for existing CFRST column. The elastic foundation beam theory was applied to CFRST column with transmission member, when solving the coefficient of concrete work by analytical method, vertical spring stiffness of steel tube was critical. Its solution was obtained by the finite element method, which was more complicated and non-intuitive for practical engineering applications, moreover, was also a certain difficulty. Defining vertical spring stiffness coefficient of steel tube, it was analyzed the various factors of the vertical spring stiffness coefficient and obtained the relationships between all influencing factors and the vertical spring stiffness coefficient. Considering the coupling effect between various factors, it was modified the fitting equation and total fitting equation. The error analysis was done. The results showed that the total fitting equation of vertical spring stiffness coefficient solved solution of the vertical spring stiffness effectively, and provided a reliable basis for the further solution of the concrete work-bearing factor.