An experimental instrument has been designed for an accurate measurement of Young’s modulus by using the principle of single-slit diffraction of light. Through the spring tension adjustment device, a bidirectional continuous adjustment can be achieved of the tensile force and real-time direct reading. Combing the micro-deformation of the wire with the optical principle, the micro-deformation of the wire can be directly and accurately measured by using a 10:1 lever based on the principle of single slit diffraction. In addition, the new instrument is characterized with such advantages as easy operation, low cost and intuitive phenomenon, which provides an innovative way to measure the Young’s modulus of materials.