Abstract: The indexing for experimental X-ray diffraction powder patterns of polycrystalline sample was performed on N-(1-naphthyl)-succinimide compound by using Materials Studio software, and the important information on crystal system, space group, and crystal lattice parameters was provided via the powder refinement and space searching processes. The simulated X-ray diffraction pattern of the calculated crystal unit cell agrees with the experimental XRD powder data. The theoretical crystal prediction of structure using the minimum energy conformation obtained by density-functional theory calculation as the input molecular structure, can afford a series of the hypothetical crystal structures in P212121 space group. It can be found that the parameters of the crystal unit cell, agreeing with both the result from powder indexing calculation and the single-crystal data, have been obtained by the refinement against experimental powder X-ray diffraction data of the polycrystalline sample of N-(1-naphthyl)-succinimide.