Using the molecular dynamics simulation method, the microstructure of the distortion region near the curved amorphous-like grain boundary in nano-NiAl alloy is studied. The results show that due to the inteal elastic force of the high-energy grain boundary, a distortion layer exists between the grain and grain boundary. The lattice expansion and the decreasing structure factor are observed in this region. The stacking fault in samples with a grain size of 3.8 nm is clearly observed across the distortion region at the site very close to the grain. The inItuences of different grain sizes on average distortion degree and volume fractions of the distortion region, grain and grain boundary are also discussed.