On-line testing apparatus for surface fault of grey cloth

The invention relates to an online detection device for defects on a grey cloth surface. A host computer is connected with a slave computer through the Ethernet, a video camera group is arranged in a video camera case, each video camera is connected with the slave computer through an image collecting card arranged in the slave computer; the slave computer receives the host computer command, starts image collection, processes the collected image information and sends image data and image processing result information to the host computer; the host computer is connected with a defect marking machine which is controlled and driven by the host computer to selvedge-mark the image defects; a rotary encoder is arranged on the same axis with a lower cloth rewinder roll through an resilient coupling, a high-power LED strip array is arranged on a side surface of an upper cloth rewinder roll and is connected with a machine frame used for fixing the upper cloth rewinder roll through a moving hinge, the single-side positive-direction high-angle off-axis illumination is adopted, the LED strip array forms an angle Theta' with the shooting axis of the video camera group, wherein the angle Theta' is less than 40 DEG and larger than 15 DEG, and the LED strip array can carry out swing positioning by the angle Theta being 25 DEG around a cloth rewinder roll axis.