The invention provides a SAPMAC method for preparing sapphire single-crystal with size above 300mm. In a 300mm sapphire single-crystal growing furnace, technical processes of charging as well as melting material, seeding, shouldering, isometric growing, pulling out, cooling, annealing and discharging are finished. On the basis of the existing SAPMAC method, the invention is greatly improved, so that the SAPMAC method of the invention has the advantages of larger size of crystal, higher quality, more reasonable size, higher utilization rate of material, lower unit production cost and the like, and can produce sapphire single-crystal with the size above Phi320*260mm, high purity, low defect density and favorable optical performance; in addition, the SAPMAC method of the invention can better satisfy demand of sapphire single-crystal with large size and high quality by national defense and military industry field as well as civil field, and reduces defect occurrence probability by controlling seeding structure; meanwhile, the SAPMAC method of the invention controls crystal shoulder structure, decreases shoulder stress and lowers possibility of crystal cleavage by changing pulling speed and cooling rate.