This study presents the effectiveness of a composite structure at improving blast resistance. The proposed composite structure consists of carbon fiber reinforced polymer (CFRP) and steel layers. While CFRP layer is used for blast energy reflection due to its high strength, steel layer is used for blast energy absorption due to its high ductility. A dynamic model is used to simulate the elastoplastic behavior of the proposed composite structure subject to blast load. Considering the magnitude variations of a blast event, the probability of failure of each layer is evaluated using reliability analysis. By assigning design probability of failure of each layer in the composite structure, the thickness of layers is optimized. A case study for the design of CFRP-steel composite structure subjected to an uncertain blast event is also presented.