This paper describes the design and realization of a metal surface cleanliness tester based on UV fluorescence method. Firstly, it introduces the importance of metal surface cleanliness testing and the limitations of the existing testing methods, and highlights the advantages of the UV fluorescence method in this field and the main features of the product. Then, the detection principle of UV fluorescence method is introduced, and the overall design architecture of the tester is described, including hardware design and core circuit design, software design and mathematical modeling methods. Finally, by showing some specific on-site application cases, its accuracy and reliability in different metal materials, different types and degrees of contamination are fully illustrated, which provides an effective technical means for the rapid and accurate detection of metal surface cleanliness, and has an important application value in industrial production, quality control and other related fields.