The invention discloses an optical fiber appearance defect detecting and outer diameter measuring device based on machine vision. The optical fiber appearance defect detecting and outer diameter measuring device comprises a machine vision detecting device, a first guide wheel used for erecting optical fiber and paying off lines, a second guide wheel used for erecting the optical fiber and taking up the lines, and at least one third guide wheel used for adjusting tension of the optical fiber. The machine vision detecting device comprises an image collecting device used for collecting optical fiber images, and a controller used for being connected with the image collecting device. The third guide wheels and the image collecting device are located between the first guide wheel and the second guide wheel. Four sets of CCD cameras are adopted for fully covering and sampling the outer diameter of the optical fiber by 360 degrees, the color uniformity of the optical fiber and the defects such as fiber missing, aramid fiber galling, surface greasy dirt, large colloidal particles adhering to the surface, stains and scratches are detected comprehensively, the missing detection rate of the defects of the optical fiber is reduced, the product quality is ensured, and the diameter of the optical fiber can be detected.