The combination of machine vision and non-destructive testing can achieve multi-dimensional evaluation of welds. This paper proposes a weld evaluation method based on the combination of line structured light and weak magnetic detection technology. The weak magnetic detection technology is used to detect the internal defects of the weld; the line structured light sensing system is used to measure the lift-off of the weak magnetic sensor and the weld, the stability of the weak magnetic detection signal is ensured, and a relationship between lift-off and peak-to-peak value model is established to provide data support for defect size discrimination; during the automatic detection process, the line structured light system is used to reconstruct the three-dimensional morphology of the weld pool surface to obtain high-precision weld profile and detect weld surface defects. The experimental device was designed and the aluminum plate weld inspection experiment was carried out. The experimental results show that the proposed method can quickly and accurately represent the weld surface morphology, and the detection effect of weak magnetic sensor on weld defects can be improved, this provides a new idea for improving the weld detection technology in practical engineering applications.