In order to study the vibration of cracked reinforced concrete beams under the load of moving vehicles more efficiently, a simulation method taking into account of the effect of crack tip closure was presented. And a coupled vibration analysis program of cracked reinforced concrete beam and vehicle load was developed on the basis of the separation analytical method. Finally, a simply supported cracked reinforced concrete beam was analyzed as an example. The results show that under the vehicle load, the change trend of deflection of reinforced concrete beams before and after the crack was the same, but the existence of cracks made it larger. When the effect of breathing crack closure, was taken into account, the stiffness of the section where the breathing crack existed changed with a "U" shape under moving vehicle load and subharmonic vibration occurred in cracked concrete beam under moving vehicle load. The variable stiffness model of concrete cracks can more truly reflect the nature of crack and can be used in dynamic analysis of cracked concrete beams. The sub-harmonic oscillation found in cracked reinforced concrete can provide a way for the identification of bridge structure crack damage.