The invention relates to a preparation method of high-speed extrusion-grade polyperfluorinated ethylene-propylene, belonging to the technical field of polyperfluorinated ethylene-propylene resin modification. The preparation method of the high-speed extrusion-grade polyperfluorinated ethylene-propylene comprises the following steps: by using tetrafluoroethylene, hexafluoropropylene and perfluoroalkyl vinyl ether as comonomers, adding a pH buffering agent, a chelator and an emulsifier into pure water, adding a fluorocarbon solvent and an initial monomer mixture, initiating polymerization reaction at certain temperature under certain pressure, and supplementing the monomer mixture in the reaction process, thereby finally obtaining the modified polyperfluorinated ethylene-propylene. The method has the advantages of simple technique, stable reaction rate and stable emulsion pH value, and lowers the volatile compounds of the polymer powder; and the prepared polyperfluorinated ethylene-propylene granules do not have the phenomenon of staining, and can be smoothly extruded and spread on the wire surface at the speed of 400-500m/minute.