CL-20/graphene foam (GF) with a guest/host architecture was obtained by in situ crystallization of CL-20 in GF. With high detonation performance (44.1 GPa, 9687 m s⁻¹), the CL-20/GF composite (98/2, w/w) is much less sensitive (IS: 4.5 J, FS: 252 N, ES: 0.72 J) than CL-20 (IS: 2.0 J, FS: 108 N, ES: 0.13 J).