Abstract: For the crack detection of long-distance natural gas pipeline, a mechanical structure of crack detector for natural gas pipeline is designed and developed on the basis of magnetostrictive effect. The structure is divided into front and rear sections, on which a consistent number of crack detector probes are installed. The front section, i.e. cup drive section, uses the driving pressure provided by the medium in the pipeline as a driving force, without influence on normal transport, and also carries a speed control system for high speed and large flow environment of large diameter pipeline. The rear section, as battery recording section, provides necessary power for equipment running and stores the signals acquired by the probes. Both sections are connected via universal joints. Through tests of the probe's mechanical performance and the whole unit's pulling, the results show that the mechanical structure has sufficient strength, and can adapt to the requirements of pipe deformation to make the probe shell close to pipeline inner wall. Moreover, the detector can effectively detect the crack defects with the length of 50 mm and the depth of 3 mm, so as to avoid security accidents like pipeline cracking caused by crack propagation.