A concrete surface crack width auxiliary measuring device is in a shovel-knife-like shape as a whole and comprises a crack width comparison plate at the head, a support in the middle and a handle at the tail, the support comprises a triangular area and a rectangular frame area, the handle is fixedly connected to one vertex angle of the triangular area, and the bottom edge of the triangular area isattached and fixed to the bottom edge of the rectangular frame area; an opening is formed in the top of the rectangular frame area, the crack width comparison plate is a rectangular plate, a standardwidth scribed line area is arranged on the rectangular plate, and a plurality of longitudinal standard width coatings are arranged on the standard width scribed line area in parallel at intervals; and the crack width comparison plate is inserted into the rectangular frame area from the top opening of the rectangular frame area and is movably connected with the rectangular frame area. The device is simple in structure, convenient and rapid to use and low in labor cost, crack information can be rapidly obtained through photographing, and heavy measurement work is converted into image data processing work; the measurement precision of the narrow crack width is improved; the application range is wide, and measurement of cracks of various heights can be dealt with.