The traditional pixel-level edge detection algorithm Canny algorithm is improved by replacing the Gaussian filter with a guided filterwhich better preserves the sharpness of edges on the basis of noise reduction and smoothingwhile designing the algorithm to adaptively obtain high and low thresholds suitable for images. An improved subpixel edge detection method based on the inverse tangent function model is proposedwhich calculates the subpixel edge position by the theory of equal area based on the centrosymmetric property of the inverse tangent functionwhich greatly reduces the computation volume and computation time compared with the traditional method. By fitting a circle with 3 times least squares to the top picture of the springthe information of the inner diameter and outer diameter dimensions of the spring is quickly and simultaneously obtained. The experimental results show that the average computation time of the proposed method is reduced to less than 1.7% while ensuring the detection accuracy compared with the traditional inverse tangent sub-pixel fitting method.