Molecular simulation technique was used to study the interaction between HMX and AP molecules. The solubility of AP in dimethyl sulfoxide (DMSO) was determined by weighing method. The solubilities of HMX in pure DMSO solvent and different concentration DMSO solutions of AP were obtained using high performance liquid chromatography (HPLC). The ternary phase diagram of HMX/AP/DMSO at 26 ℃ and normal pressure was obtained through fitting solubility data. Based on the HMX/AP/DMSO ternary phase diagram, the HMX/AP co-crystal was prepared by solvent/non-solvent method and was characterized by scanning electronic microscope (SEM) and powder x-ray diffraction (PXRD). Results show that the morphology of HMX/AP co-crystal is regular long strip and different from the original crystals (HMX, AP). The solubility of HMX/AP co-crystal in water is only 0.034 g/100 mL.