The spoke position of a wheel needs to be adjusted before the wheel-flaw detection by X-Ray machine. A method based on image processing is proposed for initial angle measurement of the spoke. Firstly, the Hough transformation is used to remove the interference information outside the wheel-circle, and then a sector sample of detection area is set on the wheel pattern image according to the number of the spokes. Finally, the tested sector detection area on the wheel is rotated, and the angle is calculated by comparing the gray scale. Experimental results show that the method can measure the initial angle of the spoke, which meets the industrial requirements.