The damage characteristics and protection performance of target structures under the combined action of air blast shock wave and high speed fragment group of fragment killing warhead are current research hotspots and difficulties in protection area. However, the present research methods and test techniques have deficiencies. Here, the equivalent shrinkage warhead whose principle is that explosive explosion drives prefabricated fragments to disperse was adopted to simulate a fragment killing warhead as a test method producing combined damage action of air blast shock wave and high speed fragment group against protective structures. On the basis of determining warhead and projectile of defensive target as well as geometric scale ratio, according to the corresponding empirical formulas of explosion mechanics, an equivalent calculation method was proposed for solving charge of the equivalent shrinkage warhead and the corresponding parameters of prefabricated fragments. It was shown that the proposed equivalent method can consider the enhanced effect of multiple fragments’ penetration and the combined damage enhanced effect of air blast shock wave and high speed fragment group; the proposed method is simple and practical with less parameters.