Expert experience is required to determine reinforcement distribution when the traditional finite element analysis method is used to analyze the composite stress characteristics of reinforced concrete box girders in earthquake environments. However, such an approach is highly subjective and will cause the deviation of the analytical results of the obtained composite force characteristics. Therefore, an experimental model of the composite force of reinforced concrete box girders under earthquake conditions is constructed. In this work, the size of the experimental model is set in accordance with previously established experimental parameters and the national restrictions on the parameters of concrete bridges. The experimental model material is selected. The continuous support of the span beam is built with round steel and angular steel, and the experimental loading scheme is designed. Then, a scientific reinforcement scheme for the experimental model of the composite force of reinforced continuous box girders in an earthquake environment is obtained. Experimental results show that the experimental model can comprehensively and accurately analyze the composite force characteristics of reinforced concrete box girders in an earthquake environment.