Abstract: Rebar truss composite floor has good mechanical properties, less formwork, and good overall performance and seismic performance, and was widely used in prefabricated steel structures. However, the beams, walls and floors were separately poured into concrete in concrete structure, and the top surface of beams or walls was not flat. The height and position of traditional composite floor were difficult to be adjusted to and reach the predetermined elevation, which affected the assembly effect and construction quality. Therefore, the height-adjustable prefabricated rebar truss composite floor was proposed. In order to study the mechanical properties of the composite floor, the accumulated strain of the reinforcement and deflection in the construction stage of two floors were measured and the static bearing capacity test in the use stage was carried out, and the crack distribution, rebar's strain and deflection of the two slabs were analyzed. The results showed that the longitudinal reinforced bars did not yield under design load, and the floor was in the stage of cracking elasticity and had a large strength surplus. From yield to failure, there was a certain safety reserve. After reaching the ultimate load, there was no brittle failure and it had good ductility. Through theoretical analysis and test results, the simplified formula of short-term stiffness of the composite floor in use stage was studied, and different calculation methods were compared.