Abstract: The interfacial slip of composite beams of steel and concrete can reduce the stiffness, increase deformation and influence performance. Experimental results of 11 samples of continuous composite beams of steel and concrete are presented in the paper, which include the law of slip and deflection of continuous composite beams. A set of analytical expressions for slip and deflection of continuous composite beam are presented by superposition method. 17 continuous composite beams are studied with the analytical expressions, and the results agree with the experimental data. It is shown that the degree of shear connection influences the deflection to a certain degree. The degree of shear connection has little influence on the deflection when full connection is reached. The increment of deflection by interfacial slip is less than 5% when the degree of connection is 0.6~1.0. Furthermore, the interfacial slip goes near to that of sandwich beam with the decrease of the degree of connection.