<p>This paper established a non-axisymmetric endwall optimization profiling platform based on genetic algorithm and designed a non-axisymmetric endwall for a transonic turbine based on the platform. The results show that compared with the original turbine cascade, the total pressure loss of turbine cascade after endwall profiling is reduced by 19.2%. Analyzing the three-dimensional flow field of the turbine cascade before and after endwall profiling, the transverse pressure gradient decreases in the upstream of the turbine cascade but increases in the downstream of the turbine cascade due to the endwall profiling. The corner vortex has a large deflection at the cascade outlet and fuses with passage vortex in the adjacent passage. This also makes the loss near the endwall region at downstream of outlet increase. In the supersonic zone, the air flows through the convex surface close to the suction surface to form a series of isentropic compression waves. The isentropic compression waves interact with the shock wave in the passage, reducing the intensity of the shock waves in the passage in the near endwall region and reducing the shock loss of the turbine cascade, which is the main reason for the reduction of the total pressure loss after the turbine cascade endwall profiling. The non-axisymmetric endwall has good adaptability at different incidence and different outlet Mach number. But when the out Mach number is lower than 0.54 or higher than 1.20, the total pressure loss could not be reduced with the non-axisymmetric endwall. When the outlet Mach number is lower than 0.54, flow in the turbine cascade is in subsonic and there is no shock wave in the passage. The transverse pressure gradient of upstream decreases while the transverse pressure gradient of downstream increases, which has little effect on secondary flow near endwall. Therefore, the total pressure loss of the turbine cascade doesn’t change obviously. When the outlet Mach number is higher than 1.20, the shock wave structure in the passage has changed, so the non-axisymmetric endwall can’t reduce the total pressure loss of the turbine cascade.</p>