Abstract: As a key part of the power system in the water-jet propulsion unit, the diffuser has the characteristics of typical large thin-walled complex curved surface structure, which requires high level on dimensional tolerance, geometrical tolerance and weight tolerance. It also requires strict control on phase proportion as well as highly compact structure. For these reasons, it's of great difficulty in casting process. However, with rational design of casting pouring, feeding and chilling system, printing the sand core with the international advanced 3 D printing technology, controlling the alloy composition and solid solution temperature, and using the AOD furnace for refining, the diffuser casting has been produced successfully at the first time. The quality meets the requirements of the control specification.