Abstract: Dynamic analysis of a RC beam system under explosion loads is performed in this paper. The beam system can be classified as the second type beam with flexible supports. Computational model for the RC beam system has been established, and then formulae for the dynamic analysis of the beam system in elastic stage and plastic stage are deduced. Governing factors and their effects on the dynamic responses of the beam system are also discussed. The study indicates that the structural vibration of the beam system depends mainly on the fundamental frequency of supporting member and the parameter . The higher the fundamental frequency and parameter , the larger the dynamic coefficient. The effect of supporting member can be neglected when ，and assumed to be rigid.