Most stereoscopic microscopes used for industrial component detection are large and have low detection efficiencies. The use of mobile phones as imaging systems (rather than conventional sensors) in industrial fields would make industrial testing more convenient. In this study, an external stereo microscope for mobile phones is designed. The proposed system can resolve details up to 0.01 mm with an 11 mm object field of view, -6.34× angular magnification, and quantitative 3D feature measurement. The combined system proposed in this paper is suitable for the microscopic observation of industrial components, with its low cost, high detection efficiency, and short installation steps.