Molybdenum disulfide (MoS₂) is of great interest due to its nanoscale characteristic size with excellent electric performance. The mechanical property is the important basis for the design and application of this novel material. In this work, we establish an atom-based molecular mechanics model with the analytical expressions to predict the elastic modulus, Poisson’s ratio and shear modulus of the single-layer MoS₂. As for the bending modulus, a loading method is proposed to construct a pure bending for this ultrathin material by molecular dynamics simulations. The results indicate that the elastic modulus, Poisson’s ratio and shear modulus of MoS₂ with infinite size are 178.9 GPa, 0.22 and 73.3GPa, respectively. It is revealed that the obvious dependence of the elastic modulus, Poisson’s ratio, shear modulus and bending modulus on the chiral direction and characteristic size. The research results of the mechanical property of MoS₂ provide an important reference for the design of the nanoscale product on the basis of this material, and also have an insight into the researches on the mechanical property of the other two dimensional materials. The supports from NSFC (11972108, 11672063, 12072061, and 12072062) and Fundamental Research Funds for the Central Universities are gratefully acknowledged.