The main span is the steel truss and the side spans are the composite truss in Minpu Bridge. A 1:2.5 model is made to study the mechanical behavior of the joint segment of steel truss and composite truss. Both a model test and a numerical finite element analysis(FEA) method have been conducted. The results show that the joint segment remains in a linear elastic state under the condition. The maximum stress in the structure is less than the material allowable strength. The FEA results are in very good agreement with those of model test. This study shows that the force transformation of the joint segment is reliable and the composition details are rational. It is also expected that the results presented in this paper would be useful as references for the further research and the design of composite truss bridge and joint segment.