The invention discloses a loss detection method for an inclined bracket pipe cap of a high-speed rail overhead line system. The method comprises the steps that the position of an inclined bracket is positioned by preprocessing an image through Hough transformation; the image is rotated until the oblique bracket is in the horizontal direction according to the inclination angle of the inclined bracket; after the edge is detected through a Canny operator, pixel gray level value accumulation is conducted on pixels located at a same vertical coordinate in the image; the edge of the inclined bracket is determined according to two peak values obtained through pixel accumulation, and then an inclined bracket image is extracted; whether the pipe cap is lost or not is judged according to a gray distribution rule of the image. According to the method, an objective, true and accurate detection and analysis result is provided, the defects of a traditional detection method are overcome, detection is easy and effective, the detection efficiency is greatly improved, and the detection accuracy is guaranteed.