The invention relates to polypropylene resin for an electrical membrane. The ash content of polypropylene resin is lower than 50 ppm; the Cl ash content is lower than 6 ppm; the MFR (melt flow rate) is 1-8 g/10 min; the isotactic index is 96%-99%; the molecular weight distribution index MW/Mn is 4-12; the polymer microstructure pentad (mmmm) is larger than 93%, and the triad (mm) is larger than 96%; the polymer melting point is 164-168 DEG C, and the crystallization temperature is 110-116 DEG C. The invention further provides a preparation method of the polypropylene resin. A catalyst with high activity and high stereo directionality is adopted, components of the catalyst have a pre-contact reaction, preferably, a pre-contact reaction product and olefin polymerization monomers perform prepolymerization, then, a propylene polymerization reaction is performed, and the polypropylene resin with low ash content, wider molecular weight distribution, high mechanical strength and good tensile property can be obtained.