The work aims to solve the technical problem that the fragile cover can both meet the strength requirements and achieve the desired breaking effect with the key to developing the fragile cover, the structure and optimal design of prefabricated stress groove. Aiming at the technical requirements of frangible cover used for a certain type storage launch box, its bearing requirements in forward and reverse directions were achieved by setting the weakening groove and coordinating with the tension-compression asymmetry of foam materials. The equi-strength groove was designed by changing the depth of weakening groove, so as to achieve the desynchronizing of multiple pieces and control the number of pieces. After the sample pieces were subject to cover punching experiments with static pressure and gas dynamic pressure, the pressure-bearing and crushing performances met the index requirements. There were no residues at the place slid by the missile wing at the cover edge. The cut-off from roots was good and the cover fragments were quite small. In such case, it indicated that the structural design of the fragile cover was reasonable and the performance met the requirements. Therefore, the methods and research results herein provide a reference for the design and application of the fragile cover.