The invention discloses a biaxially oriented polypropylene (BOPP) capacitor membrane special-purpose polypropylene composition synthesis method. The synthesis method comprises that a polypropylene base material is produced by liquid phase method polymerization under the conditions of activated magnesium chloride as a carrier, Ziegler-Natta as a main catalyst, and a cocatalyst, the polypropylene base material and an additive are mixed to obtain a uniform mixture, and the mixture is subjected to melt-blending granulation to form ultrapure polypropylene resin products for manufacture of a BOPP capacitor film. The polypropylene composition can satisfy technical requirements on BOPP capacitor film processing and guarantees excellent mechanical properties, high uniformity, high cleanability and good electrical performances of the manufactured BOPP capacitor film.