Mechanical properties have close relation with microstructure. Based on orientation of the molecule chain in fiber, they show a rapid increase in tensile properties. Nevertheless, block materials mainly gain rise of mechanical properties by blend or composite, it is hardly proposed on the self-reinforced materials by optimizing the microstructure. In this work, the structure and tensile properties of polypropylene (PP), treated at 105°C for 5min under different pressure, were studied with microscopy, differential scanning calorimetry (DSC). The variety of supra-structure that the spherulite deforms into ellipse even fractures piece in the pressure field adds to the mechanical properties. The orderliness of crystal increases with the pressure, and Tm is increased slightly from the original level.