In order to study the formation mechanism of 2,4,6-trinitrotoluene (TNT)/ 1-nitronaphthalene (NNAP) cocrystal, powder XRD, FTIR and DSC were used to study the TNT / NNAP samples after grinding at 0 s, 10 s, 20 s, 30 s, 40 s, 50 s and 2 mins. The XRD patterns showed that the new diffraction peak, corresponded to (2 -1 1) plane of TNT/NNAP cocrystal, appeared at 2θ=25.8° and gradually increased its intensity. FTIR spectrum illuminated that the C—N—O bending vibration peak (716 cm^-1) of TNT had a blue-shift and became sharp. At the same time, due to π-π stacking, the C—C bending vibration peak (734 cm^-1) of TNT benzene ring exhibited a red-shift. The DSC curves indicated there were three endotherm peaks during the formation of cocrystal. These results showed that cocrystal packed at (2 -1 1)) plane firstly. H-bond and π-π stacking played important roles in the formation of TNT/NNAP cocrystal. TNT and NNAP firstly generated two eutectics, then transferred into TNT/NNAP cocrystal. The melting point of this cocrystal is 65 ℃.