Abstract: Magnetic detection technology had generally used in the defect detection of ferromagnetic materials. In current study, a kind of weak magnetic detection technology which can be applied to the defect detection of ferromagnetic and non-ferromagnetic materials is presented. The basic principle of the technology of weak magnetic detection is introduced. Taking two kinds of non-ferromagnetic materials, polysilicon and 7A09 aluminum alloy as an example, in this paper, the general process of detecting non ferromagnetic materials by using weak magnetic detection technology has been described. Having tested material permeability, designed experiment, collected and analyzed signals. The experiments on natural defect detection of polysilicon shows that the weak magnetic detection technology can detect the inclusion defects of 10 μm diameter, and the experiments of artificial defect detection of aluminum alloy shows that the weak magnetic detection technology has a good detection effect on Φ0.4mm hole defect and groove type defect in 1 mm to 2 mm depth. The feasibility of this method in the detection of non ferromagnetic materials has been verified.