In order to solve the problem of large experimental error caused by the inability to level the tension lever during the operation of the string vibration experiment，the research has improved the string vibration device，so that the experimental error has been reduced to a large extent．The principle of reflection of light is used to overcome the large error caused by the level of the traditional string vibration experiment with the naked eye observation of the tension lever．The study shows that the relationship between the resonant frequency and the number of wave webs on the string is reduced by 1．94% on average by the improved experimental setup，which well verifies the feasibility and effectiveness of the improved scheme．