The invention discloses a method for determining the polypropylene fiber content of building mortar and belongs to the technical field of building materials. The method includes: preparing a sample, stirring, aging, separating, extracting, neutralizing, filtering, drying and calculating. The method for determining the polypropylene fiber content of the building mortar has the advantages that the method is put forward for the first time, the polypropylene fiber content of the building mortar is determined, the problems that the content of polypropylene fibers inside the hardened dry-mixed mortar cannot be detected and the quality control of the dry-mixed mortar is in severe time lag are solved, data is provided quantitatively, and the method is significant to the quality guaranteeing of the mortar; the method is simple to operate, convenient in determining, high in accuracy and low in cost.