The co-crystal of hexanitrohexaazaisowurtzitane （CL-20） and 2，4-dinitro-2，4-diazapentane （DMMD） was prepared by co-crystallization in solution. It was characterized by single crystal X-ray diffraction（SCXRD）， scanning electron microscopy（SEM）， powder X-ray diffraction（PXRD）， and fourier transform infrared （FT-IR）， and differential scanning calorimetry （DSC）. The results show that CL-20/DMMD co-crystal belongs to monoclinic system with space P2₁/c. Analysis of interactions in co-crystal shows that the main forces between two kinds of molecule in co-crystal are hydrogen bonds and features a layered motif. There is new crystal phase in the XRD pattern. The shift of peaks for CL-20/DMMD attributes to the formation of C─H…O hydrogen bonding in FT-IR pattern. Results of DSC show that the melting point of co-crystal is 180.8 ℃， which is 21.5 ℃ and 120.9 ℃ higher than that of CL-20 and DMMD. The main thermal decomposition peak temperature of CL-20/DMMD co-crystal is 240.1 ℃， which increases by 3.5 ℃ compared with CL-20. The predicted detonation velocity and detonation pressure of CL-20/DMMD co-crystal are 9386 m·s^-1 and 45.09 GPa according to the theories of Rothstein and Petersen， respectively. They are slightly lower than that of CL-20 and higher that of DMMD（D=7287 m·s^-1，P=21.79 GPa），HMX（D=9048 m·s^-1，P=40.55 GPa）， RDX（D=8945 m·s^-1， P=37.28 GPa）， and TNT（7042 m·s^-1， P=21.44 GPa）.