The invention discloses a process design method of an upper casting for a large ship, which is formed by optimizing on the basis of an existing process. The process design method comprises the following steps that (1), the linear shrinkage is selected as 1.8%-2.0%; (2), cutter leveling is additionally carried out a rib plate of a welding steel plate making contact with a ship body; (3), a processcorrection amount is added to the rib plate; (4), an air exhaust steel pipe is horizontally placed in the middle of a loam core, straw ropes are wound outside peripheral cutting holes, and a wood realsample is subjected to pattern draft according to a ratio of 1:20; (5), a riser is designed by adopting a hot pitch circle method, and spot casting is carried out at the riser; (6), upper and lower middle surfaces are selected as parting surfaces; (7), sand-hanging external chill is horizontally placed on the back surface of the riser; and (8), proper wrapping holes and quantity are selected according to gross weight and maximum height of the casting. By the adoption of the process design method, the casting quality of the upper casting can be guaranteed, the using requirement of a shipyard is met, meanwhile, the production efficiency is improved, the production cost is reduced, and the process design method is suitable for lower castings, upper and lower rudder knobs, rudder stock bearings and dumb braces.