Warheads full-scale fragment field has great significance to military production and storage safety. In this paper, an improved Continuum-Discontinuum Element Method (CDEM) will be used for the first time to solve the problems of large deformation and cross-scale calculations for warheads, describing the complete process from casing breakage to fragment scattering and landing. A fragment equivalent layer-detonation product escape algorithm is further introduced to increase calculation efficiency, and the fragmentation field is post-processed using a penetrable virtual target board algorithm. This method simulates warhead fragmentation in the full space-time domain, laying a foundation for subsequent study of questions like warhead fragmentation safety distance and fuze delay arming time. Comparison with warhead static explosion and ballistic gun testing data verify the effectiveness of this method.