Noble metal nanoparticles are attractive catalytic materials because of the excellent physical and chemical properties. However, the structural stability and hydrogenation mechanism of NiPt nanoparticle are not entirely unclear due to the structural feature. We apply the first-principles calculations to study the structure, mechanical and electronic properties of NiPt nanoparticle. In particular, the hydrogenation mechanism of NiPt is studied. Here, four nanoparticles (line, ladder, saw tooth and triangular) and three crystal structures (cubic and tetragonal) are considered. The calculated results show that the crystal NiPt is more thermodynamically stable than the nanoparticles. We first find that the NiPt with tetragonal structure (P4/mmm) is a stable phase among these crystal structures. The calculated lattice parameters of the tetragonal NiPt area= 2.731 angstrom andc= 3.664 angstrom. In addition, the tetragonal structure is mechanically stable. In particular, it is found that the hydrogen (H) occupies the octahedral interstice site in comparison to the tetrahedral interstice site. Essentially, the hydrogenation behavior of NiPt is attributed to the strong hybridization between H and NiPt.