To clarify the structural behavior of composite slab with steel bar trusses at key construction stages including hoisting and concrete post-pouring, a composite beam bridge with a main span of 60 m in Georgia’s E60 Highway was investigated. A finite element model was developed by using ABAQUS to simulate the construction process and analyze the influence of parameters such as prefabricated bottom slab material, number of hoisting points, slab thickness, and number of steel bar trusses on the principal stress of concrete and mid-span deflection. The results indicate that ultra-high-performance concrete (UHPC) prefabricated bottom slabs prevent plastic damage and enhance slab stiffness. Normal concrete (NC) prefabricated bottom slabs should set six or more hoisting points, while UHPC prefabricated bottom slabs require only four hoisting points. Increasing slab thickness can raise the concrete’s maximum principal stress at the hoisting stage, but it has a negligible impact at the concrete post-pouring stage. Increasing the number of steel bar trusses in the prefabricated bottom slabs can reduce the concrete’s maximum principal stress at the hoisting stage, and both the concrete’s maximum principal stress and mid-span deflection decrease at the concrete post-pouring stage with the increase in the number of steel bar trusses. These research findings may provide a reference for the hoisting and concrete post-pouring of composite slabs with steel bar trusses and support the actual application of UHPC-NC composite slabs.