The 650 rolling milling machine of a steel mill is open train with three mills. Blanks of 120，140，150，160 and 170 cubic meters should be fed to the second and the third mill during the milling of round steel of Φ80-Φ160 mm，therefore the rollers of the first mill need to be changed frequently so as to change the pass. Frequent roller changing affects the production efficiency severely with small production quantity. The optimized design is that the big size blanks of 160 cubic meters supplied by the first 650 mill passes through the flat box hole and vertical stamping hole in the universal round hole patterns of Φ125-Φ130 mm of the second mill，and then it was fed into the flat hole, vertical stamping hole and oval hole in the universal round hole patterns of Φ115-Φ120 mm，eventually into the third mill for end rolling product. Through the theory verification and production practice of rolling mill pass optimization design，the new pass system was proved to be feasible, and it ould improve production efficiency and reduce labor intensity of workers.