Abstract: Based on the test of the reinforced concrete column-steel beam ( RCS)，load-displacement hysteresis curves of three RCS composite joints with different details were analyzed． According to the test result，a uniform skeleton curve，expressed by trilinear model was established by using regression analysis． As well as，the equation of the skeleton curve divided by six parts was given respectively． The stiffness degradation rules of RCS joints were got through regressive analysis of the circulations in different loading stages． Then the restoring force model of the ＲCS composite joints was obtained． Examples showed that the skeleton curves calculated by the restoring force model coincided well with the test curves． Which also showed that the restoring force model had a good applicability．