The invention provides a polypropylene. The content of internal compensation five-unit group (mmmm) measured by nuclear magnetic resonance (NMR) spectroscopy of the polypropylene is 70 to 80 mol%, and the content of internal compensation three-unit group (mm) is 75 to 85 mol%. The invention also provides a preparation method of the polypropylene. According to the preparation method, in the presence of a supported metallocene catalyst and second alkyl aluminoxane, propylene is polymerized, wherein the supported metallocene catalyst comprises a carrier, metallocene compounds loaded on the carrier, alkyl aluminium, and first alkyl aluminoxane, the chemical formula of the metallocene compounds is rac-R1<2>-Si(2-R2-4-Ar-Ind)2MX2, in the chemical formula, the R1 and R2 individually represent a C1-C5 alkyl group, the Ar represents an aryl group, the Ind represents an indenyl group, the M represents titanium, zirconium or hafnium; and the X represents a halogen atom. The provided polypropylene has the advantages of low haze value and good transparency.