Density functional theory calculations were performed on crystalline 2,6-diamino-3,5-dinitropyridine-1-oxide (ANPyO). The conduct bands are generally quite flat, while the valence bands are uneven. The carbon, oxygen and amino nitrogen atoms make up the narrow lower energy levels. While the carbon, amino nitrogen and atoms in nitro group make up the higher energy levels. Change of electronic charges for the decrease of the cell edge a and c are almost the same, but different from the decrease of the cell edge b, indicating an anisotropic effect related to compressions. The C-Nitro and the N-O (N-oxide) bonds are the weakest, and tend to rupture upon external stimulation. The Mulliken population for the N-O (N-oxide) bond in crystal is much smaller than that in molecule, indicating that the molecular packing weakens this bond. Judged by the fact of N-O (N-oxide) bond being weaker than C-Nitro bond, ANPyO is sensitive to mechanic impact than 1,3,5-triamino-2,4,6-trinitrobenzene, which is in good agreement with experiment. The crystal lattice energy is predicted to be -166.03 kJ/mol, after being corrected for basis set superposition error.