The parameter measurement method of straight spur gear was studied by using MATLAB image processing technology. The gear image was obtained by using the machine vision system, and the image was grayed, denoised and binarized. The region of gear hole was found and removed according to 8 neighborhoods, and the edge detection was carried out by using the Canny operator. The diameter of the gear hole was obtained by calculating the minimum rectangular size containing the gear hole profile. The single-pixel outer profile of the gear was obtained by using 8 neighborhoods boundary tracking method. Position points of addendum and dedendum were found by using the classification method of outer profile points based on neural network. The diameters of the addendum circle and dedendum circle were calculated by using the circle fitting method based on the least square principle. The number of teeth was determined by using the method of calculating 8 connected regions after expansion operation of the addendum or dedendum image. The modulus was calculated by the addendum circle formula. Gear parameter measurement software was prepared and the parameters of 6 straight spur gears were measured. The rationality of the method was verified by comparing with the theoretical value