In order to establish a numerical model of the structural damage effect under the combined loading of blast and fragments, this paper investigates the physical characteristics of three kinds of damage elements, namely, fragments, detonation products and air shock waves, produced by the explosion of a cased charge. According to the law of energy conservation, a more reasonable method is proposed to evaluate the velocity of fragments. Considering the crushing energy of casing and the kinetic energy of fragments, the shock wave produced by the explosion of the cased charge is equal to the shock wave produced by the explosion of a given amount of bare charge, and a corresponding solution formula is given. Based on the solution formula for shock waves, this paper proposes a combined theoretical and numerical finite element analysis method to evaluate the damage effects of walls under the combined loading of blast and fragments. The results of the study show that there is good agreement between the experimental and numerical analyses.