To study further the bearing capacity of square steel tube columns filled with steel reinforced concrete, several broken modes were divided based on the changing of neutral axial. Bearing capacity computation formula was deduced by stirrup method. Amplified coefficient of eccentricity was regressed based on computed results of nonlinear program, and mid-long columns capacity was deduced. Input the computation formula into Excel, capacity was calculated by exhaustion the compression zone depth of concrete. Calculation results were agreed well with the tested ones.