Abstract: In order to reduce aerodynamic loss caused by large meridional expansion angle, orthogonal optimization and numerical simulation methods were used to study the optimal modification laws of blades with bending, twisting, and bend-twist compound modifications at different meridional expansion angles based on the principle of optimal matching of stator blade and rotor blade, and their effects on aerodynamic performance of turbines were analyzed. Results show that the three blade modifications can effectively reduce the secondary flow in the hub endwall and the main-flow region, and improve the aerodynamic performance of the turbine. With peripheral efficiency as the optimization objective, the optimal bend form of the stator blade is inverted bending at both ends and positive bending in the middle at each expansion angle. The greater the expansion angle, the more significant the efficiency improvement. When the expansion angle is 36°, the peripheral efficiency can be improved by 5.43%. The twisting modification has the best effect on improving the peripheral efficiency, which can be increased by more than 6.00% at each expansion angle. However, it will greatly reduce the flow capacity of the turbine, and increasing the expansion angle can offset the negative effect caused by twist. When the expansion angle is less than 24°, the bend-twist compound modification can maintain good flow capacity while ensuring high efficiency, and its optimization effect is better than that of the single bending or twisting modification.