In order to study the mechanical characteristics of composite girder bridge under mid span wheel load, the experiment and numerical simulation of largescale steelconcrete composite girder bridge were carried out. Through the threepoint loading test, the stress state of the steelconcrete composite beam under the fixed wheel load in the middle of the span was simulated, and the actual contact deformation resulted from the wheel loading and the actual constraint effect of the beam end support were considered, the finite element numerical simulation analysis of the test was carried out. The reinforced concrete bridge deck, steel beam, shear connection stud and bearing were modeled and calculated respectively. The load displacement curve of the composite beam under the mid span wheel load was obtained. Combined with the numerical simulation method, the stressstrain changes and the crack development of the concrete slab under different loading conditions were analyzed. The results verify the accuracy of the numerical simulation method in the composite beam stress simulation, clarify the failure characteristics and stress state of the composite beam under the fixed point loading in the middle of the span, and accurately analyze the stress characteristics of the simply supported steelconcrete composite beam under the concentrated wheel load in the middle of the span.