Effects of geminal and vicinal delocalization (hyperconjugative interactions) on the structures of disilyne (HSi drop SiH) and its derivatives were investigated by deleting those hyperconjugative interactions in density functional theory (DFT) calculations. It is concluded that the hyperconjugative interactions are effective for the structural preference of disilyne, and that geminal delocalization are dominant. We found that two geminal delocalizations affect the structural preference of disilyne and its derivatives. One gives trans bending structure and the other gives single bond type structure. Although the status of natural bond orbitals (NBO) and the NBO scheme used for the deletion of hyperconjugative interaction is unclear in general, our present conclusion is true within the NBO method.