The invention discloses a method for machining a shell liner of a shell in a semi-autogenous mill. A lifting strip is arranged in the center of the shell liner, the upper portion of the lifting strip is arranged to be a right angle, the lower portion of the lifting strip is arranged to be an obtuse angle, reinforcing ribs and lifting holes are symmetrically and evenly distributed in the two sides of the lifting strip, the shell liner is made of ultrahigh manganese steel alloy, according to the formula, the alloy comprises, by weight, 1.0-1.4% of carbon, 17-19% of manganese, less than 0.05% of phosphorus, 0.3-1.0% of silicon, less than 0.05% of sulphur, less than 0.2% of aluminum, less than 0.5% of vanadium, 1.5-2.5% of chrome, less than or equal to 1.5% of nickel, less than or equal to 0.5-1% of copper, 0.3-1.0% of molybdenum, a micro amount of bohemium, and the balance iron. According to the method, the material formula is changed, the structure of the shell liner is designed, the thermal treatment process is optimized, the whole intensity and hardness of the shell liner are improved, and the mechanical performance of the equipment is met. The labor intensity is reduced, the service life of the equipment is prolonged by at least more than six months, and the economic benefits are improved.