The experiment is based on the improved Jolly’s scale，and a device for measuring stiffness coefficient using Hooke’s law is designed by using the principle of optical lever．The device obtains the rotation angle of the lever by recording the distance between the initial and final positions of light movement，calculates the extension length of the measured spring．The experiment overcomes the influence of the deadweight of the spring，reduces the measurement error，makes the experimental phenomenon more intuitive，and enhances the experimental measurement accuracy．