Hydro turbine blade castings are susceptible to distortion during heat treatment process due to their thin and curved shapes. By the numerical simulation method, the displacement results of the castings can be acquired. However, the displacement consists of distortion and contraction or expansion and depends on the selection of reference points which are hard to be exactly selected. In this paper, a distortion evaluation method is presented, in which the curvature variation of local areas with respect to the original shape is utilized. By adding the displacement results, the finite element model at each step is converted into STL format files. Then, based on the STL files, the curvature around each vertex is calculated and the curvature variation of each step relative the original shape is acquired for the description of distortion. The distortion degree of the whole casting is evaluated by the local variation of curvature, which is independent on references points and also suitable for the evaluation of distortion during heat treating process. Reference points can be selected in the areas with smallest distortion, which can be used for the displacement evaluation.