The utility model discloses a rail type drilling peeping device which is characterized in that a sliding rail assembly comprises a plurality of sliding rail parts which are correspondingly spliced together end to end, each sliding rail part comprises two parallel rails, and the two rails are connected together through an X-shaped adjustable rail support; the peeping probe is arranged on an X-shaped adjustable pulley support, pulleys are arranged at the two ends of the X-shaped adjustable pulley support respectively, and the cross connection position of the two pulley fixing rods is fixed to the side wall of the peeping probe. Pulleys at the two ends of the pulley fixing rod can be matched with the two rails of the sliding rail part respectively and slide along the rails. The peeping instrument is convenient to install, the peeping instrument can be kept in the center of a drilled hole in the using process, view finding deviation of the peeping probe in the drilling process is avoided,a good detection scene is guaranteed, the peeping effect is improved, and the peeping probe cannot be clamped in the drilled hole. The peeping instrument is convenient to assemble and disassemble, thepeeping instrument can be easily and directly fed into a drill hole through the rail, and the peeping efficiency is improved.