Abstract: Aircraft hydraulic system conduits are subject to under great pressure, which is a key component of the aircraft pipeline's compression resistance. This study proposes a weak magnetic detection technology based on the geomagnetic field environment to solve aircraft duct crack defects. Firstly, the principle of weak-magnetic detection was introduced and the magnetic field characteristics of aircraft duct crack defects are simulated and analyzed using by COMSOL Multiphysics simulation software. Then the feasibility of weak-magnetic detection of aircraft duct crack defects is theoretically proved. After that, an independently developed high-precision fluxgate sensor was used to test the aircraft catheter test specimens containing artificial prefabricated crack defects, and the detection signals were processed. In order to improve the signal-to-noise ratio of the defect, the detection signal was subjected to magnetic gradient calculation and the 3σ method in the normal distribution is used to judge the defect, so that the detection effect of the defect is significantly improved. The results of simulation analysis and testing experiments show that for artificial crack defects with a depth greater than 0.1 mm, the weak-magnetic detection technology has a good detection rate, which verifies the feasibility of the weak-magnetic detection technology in aircraft duct defect detection.