The invention discloses a method for preparing pork pig feed by adopting banana leaf sheath as a main raw material. The pork pig feed is prepared by the following raw materials in parts by weight: 53 to 58 parts of banana leaf sheath powder, 28 to 32 parts of corn powder, 8 to 12 parts of wheat bran and 4 to 6 parts of Chinese pennisetum. The method comprises the following steps: (1) selecting raw materials: after bananas are harvested, stripping the banana leaf sheath one by one, and removing rotten and turned leaf sheath and other impurities; (2) treating raw materials: crushing the banana leaf sheath obtained in the step (1), placing the crushed banana leaf sheath into a fermenting tank, adjusting the pH value to be 6.5 to 7.0 to obtain fermented liquid, introducing mature lactic acid bacteria liquid strain, adding pectinase, stirring, standing, fermenting, and taking out and draining to obtain banana leaf sheath powder; (3) mixing: crushing the Chinese pennisetum, adding the corn powder, the wheat bran and the banana leaf sheath powder obtained in the step (2), and mixing according to a ratio; (4) drying: drying the mixed material, and packaging the mixed material to obtain a finished product. By adopting the method, while the meat quality and the fattening time are guaranteed, the raising cost is obviously reduced, the breeding benefit of pigs can be obviously increased, and the breeding benefit can be improved by 25 percent or more compared with the traditional breeding technology.