A three-dimensional grid model was established to simulate filling process of the rudder in squeezing casting based on practical rudder dimension and technique design, in which relevant boundary conditions were considered. Simulated results show that the converging point of pressure flow and reflect flow in filling process in squeezing casting lies at the top right sides of the rudder, accompanying with the appearance of turbulent flow and entrapped-gas. The practical produced rudder shows that its top right sides are a place where most casting defects occur. Simulated results are well in agreement with practical ones.