Based on the fact that in the clamping robot for three jaw chuck in numerical control (NC) machine tools, the clamping robot with vision system has high demand for recognition and position, a novel subpixel location method in which the Gaussian quadratic curve fitting is under the centroid guidance was put forward. The procedures were as follows. Firstly, the rough edge, as the pixel level edge, was achieved by the Canny algorithm. Secondly, the centroid determined by the centre of incircle and circumcircle in three-jaw chuck was established. Thirdly, referring to the geometrical characteristics and the gray distribution characteristics of neighborhood pixels, the subpixel level location was completed under the centroid guidance. At last, the experiment was made. The results show that vision measuring accuracy reaches 0.01 mm, and positioning accuracy reaches 0.05 mm, which satisfies the NC machining requirements. This technology guarantees machining accuracy, and greatly improves the computational efficiency.