NIL(Nano Imprint Lithography) is one of the most promising lithography techniques. There are many variants of NIL, and two major techniques of them are thermal NIL and UV NIL. Here, we focus ourselves on the thermal NIL. During the thermal NIL, the polymeric patterns experience large mechanical strain and high temperature, and this often leads to malformation of polymeric patterns. So it is needed to improve the pattern fidelity and contrast, and these are believed to be closely related to the process condition and mechanical properties. In thermal NIL, PMMA is widely used and chosen as target polymer. Generally, mechanical properties in nano scale are really hard to acquire. In this study, we estimate the mechanical properties of PMMA by molecular dynamic simulation. These properties will be used as input of continuum simulation. We will estimate stress-strain relationship of PMMA. This stress-strain relationship depends on strain rate and temperature. So we will study about strain rate and temperature effect.