The invention discloses a dry net deviation detector. The dry net deviation detector comprises a mounting seat, a base, a support arm, a slide arm, a branch arm, a detecting seat and a winding reel. The base is mounted in the mounting seat. The support arm is mounted at the center of the top of the base. A first insertion groove is formed in one side of the support arm. A gear box is mounted at the top end of the support arm. First threaded rods are mounted at the top of the base and on the periphery of the support arm. The top ends of the first threaded rods penetrate the slide arm, and driven wheels located in the gear box are mounted at the top ends of the first threaded rods. A rotating shaft is mounted at the internal center of the gear box. The dry net deviation detector has the advantages that dry net deviation interference signals generated by limited vibration sources can be effectively prevented, and accordingly, safety and production stability of dry nets are ensured; height and length adjustment of detected portions is rapidly completed, local adjustment after mounting of the detector is facilitated, re-disassembly and re-assembly are not needed, and the length of a guide line is adjusted conveniently during overall adjustment of the detector.