In the manufacturing process of aluminum foil, gold foil, etc., there will be a certain proportion of defective products. The typical defect is a tiny void, and the size of the defect is very small, usually at the μm level, which cannot be directly judged by the human eyes. A non-contact system device for detecting tiny defects by combining the highly collimated narrow-band line light source and a large field of view receiving optical system was proposed. The system consisted of the laser light source, a Powell prism, and an aspheric lens to output a highly-collimated, highly-uniform, and large-sized linear laser beam. The linear array detector was placed on the defocus plane of the focusing lens, and the specific location of the defect could be determined by the position of the received light spot. According to the intensity of the light, the size of the defect aperture could be identified, and finally the location and classification of the defect could be achieved. The system realized the detection of large-size products and μm-level tiny defects, and has non-contact, fast, and accurate automatic detection capabilities, which effectively solves the problems of low efficiency, high difficulty, high missed detection rate, and high cost when manually detecting tiny defects.