Abstract: Explicit central difference method for dynamics was applied to parametric analysis on the mechanical constitutive relationship of automotive polypropylene (PP) material. The tensile testing was carried out to obtain the tensile curves at four strain rates. The method of combining Cowper-Symonds model and finite element dynamic caculation was used to analyze the above curves, and then mechanical costitutive relationship parameters of PP material were obtained. The results show that the method could predict mechanical costitutive relationship parameters of PP material accurately, the strain rate parameters C and P were 179.25 and 4.6, respectively. The elastic modulus, yield value and fitting formula of stress-effective plastic strain curves for PP material in static tension were obtained, constitutive relationship parameters based on Cowper-Symonds model were obtained.