Abstract: Premade fragment warhead has the advantage of almost 100 percent control of the fragment mass and shape, but the acceleration velocity of the fragment will be affected by the early leakage of detonation product. In order to analyze the influence of gas leakage on the fragment lethality, numerical modeling was used to study the leakage process of certain premade fragment warhead and computing results from different algorithms were compared with the experiment. The results show that when initiated at one end center, the gas leakage mainly happens circumferentially, having a huge influence on the fragment dispersions. The fragment velocities and ejection angles results of fluid-solid couple algorithm agree best with the experiment results, with the least relative errors of 1.12% and 0.56% respectively. Given the robustness, precision, and time of calculation, the fluid-solid algorithm is a reliable tool for studying the gas leakage of warhead.