By using molecular dynamics (MD) method, the tensile behavior of ultra-thin ZnOnanowires in <0001 > orientation with three different diameters have been investigated respectively. Through the numerical simulations, the tensile properties including Young’s modulus and yielding stress are obtained as functions of strain rates, temperatures and diameter sizes. The simulation results indicate that the nanowire Young’s modulus and yielding stress would decrease with the increasing of diameter size. In addition, a significant dependence of tensile properties on temperature was also observed with the Young’s modulus and yielding stress decreasing on average by 8% and 18% respectively, while the temperature rises from 0.1 K to 400 K. However, in our simulations the Young’s modulus and yielding stress have no obvious change with different strain rates. Lastly, the structure of ultra-thin ZnOnanowires could be transformed at the strain of ∼7%-11% while the nanowires eventually fracture at the strain of nearly 15%.