Abstract: High-altitude balloon has attracted much attention because of its wide application fields, and its production process requires strict control of key quality links, material selection and welding of ball film. Compared with the material quality of the whole ball film, the welding part is more fragile, which is easy to cause the failure of the ball structure due to weld defects, resulting in serious flight accidents. Aiming at common basic weld defects, a method of weld defect detection based on polarization sampling and target contour marking was proposed. On the basis of applying polarized light to enhance the contrast of weld defect position in the image, sample collection was carried out, and after image preprocessing and threshold segmentation, defect contour features were marked, and the contour features were equivalent to defect features, and the defect features were digitized, so as to detect different kinds of weld defects. Experimental results show that the method can detect three typical defects in weld production samples, with an accuracy of 91.37%. It has high processing efficiency, short response time, convenient data tracking, and obvious output results, which can replace traditional manual detection and realize the purpose of efficient detection of ball film weld defects.