We proposed a new concept "green high energy density material" (HEDM) and designed some N2H2O isomers, i.e. oxadiaziridines (1a, 1b), diimide N-oxides (2a, 2b), hydroxydimides (4a, 4b) and nitrosoamide (5). These isomers satisfy the following conditions: (i) they have high energy densities; (ii) they have considerable kinetic stability; (iii) their green channels are favored more than non-green channels; and (iv) they have high possibility to be actually synthesized for practical use. The very high energy densities of oxadiaziridines (1a, 1b) and the outstanding kinetic stability of diimide N-oxides (2a, 2b) are strongly encouraging the first realization of green HEDM.