Abstract: Taking a φ1100 mm lower ring of hydraulic turbine as the research object, two gating system schemes(bottom pouring and middle pouring) were designed. Numerical simulation was adopted to analyze the filling temperature field and internal casting defects of castings with different gating systems under two pouring velocities of 30 cm/s and 40 cm/s. The results show that for the middle-pouring gating system at a pouring velocity of 30 cm/s, the temperature variation range of the hydraulic turbine lower ring casting is smaller, the casting exhibits the fewest defects, more uniform internal grain size and nucleation density, and milder compositional segregation.