A new method to evaluate the freeform surface error is proposed in this paper. Testing whether the error is within the required tolerance zone is implemented by comparing the reconstructed machined surface with the design surface. The inspection process is created out by these steps: acquisition of measurement points on the actual surface, transform the measurement points from the measurement coordinate system to design coordinate system by location; the machined surface is reconstructed by the located points based on Bspline interpolation; the reconstructed surface is compared with the design surface. Because of the uncertainty in measurement process, the uncertainty of location, reconstruction, and form error are analyzed. The proposed method is verified in the measuring and analysis of “S” shape test shape. The results show that the proposed method is effective to guide the evaluation and acceptance of free form surface machining quality.