Non-axisymmetric endwall is numerically investigated to suppress the secondary endwall flow in a HP turbine suction surface. The endwall contour is represented by a non-uniform rational B-spline surface. Two solution spaces are designed by the rule of hypercube sampling through variation of nodal radial extension. Final most effective endwall contour is obtained through screening all available samples with surrogate-based model. Results show that non axisymmetric endwall reduces the turbulence kinetic energy of the passage vortex by 5.5％and the total pressure loss 1.6％. Local heat transfer coefficient is lowered on the afore passage endwall surface with a certain increment on the aft passage endwall. Overall averaged heat transfer coefficient is reduced.