The gaseous isomers and crystalline state of carbohydrazide (CHZ) were studied at the DFT-B3LYP/6-31G^** level. Three stable isomers were located. The structure Ⅱ，which is in agreement with the structure in the crystal，is the most stable. The vibrational frequencies were analyzed and they agree well with the experimental results. The terminal nitrogen atom of the hydrazine group and oxygen atom of the carbonyl group are preferable coordination sites for CHZ molecule and this was demonstrated by the experimental results. The intermolecular interaction is strong in the crystal. Furthermore，all of the atoms have contributions to the frontier bands. Some bands are very oscillatory，which show that the corresponding molecular orbitals are strongly perturbed by the crystalline environment.