In order to solve the problem of low accuracy caused by false and missed detection in the corner detection methods of current visual measurement of thread key parameters, we proposed a new method based on contour corner detection. Firstly, bilateral filtering and iterative threshold method are used to improve the Canny operator to increase the accuracy of edge detection. Secondly, the doublethreshold DP algorithm and Hough transform were used for piecewise fitting; the edges are protected and Contour smoothness is kept. Furthermore, the corner points of the tip and bottom of threads were extracted with CTAR algorithm. Finally, thread major diameter and minor diameter is measured according to the position information of corner points. Experimental results show that, compared with the traditional Canny operator and Harris corner detection method, our new method can accurately and reliably detect the thread edges and corners. Therefore, the high precision measurement of screw thread parameters is realized. The average measurement accuracy of major and minor diameters of screw thread is 0. 003 3 mm and 0. 002 6 mm, respectively.