Abstract: To calculate the creep effects of steel-concrete composite beams under support constraints, and to predict the long-term mechanical properties, the coupling relationship between sectional stress redistribution in the continuous composite beams and restrained internal force redistribution of structural supports was unlocked based on the principle of force method and creep constitutive equation of concrete. The analytical formulas for computing the creep secondary internal forces of the composite beam under the two conditions of fast and slow support constraints were deduced. Then, both of theoretical and numerical methods were adopted to analyze an example. The calculation results show that, the creep plays a beneficial role in restricting the settlement of support. The creep secondary moment in the steel-concrete composite beam is affected by the internal stress redistribution, can be controlled by the redistribution coefficient, and varies with the stiffness ratio between concrete and steel beam. The internal stress and external internal force can influence each other. This change process is related to the creep coefficient and aging coefficient. These formulas derived in this paper are proposed based on clear mechanics concepts. Therefore, this method can be more conveniently used to calculate the internal forces of the steel-concrete composite beams under the influence of bearing changes. The obtained results can effectively reflect the mechanics characteristics of steel-concrete composite beams. This method is an effective supplement to evaluate the long-term mechanical characteristics of the composite beams.