Abstract: Standing wave experiment is one of experiments of college physics. Comparing to the tuning fork in the earlier time,metallic string is applied in the new experimental instruments.The standing waves can not only be observed on the string,but also the voice of string vibration can be heard. It will be convenient to study the relationship between vibration and voice,and this will help to understand the mechanics of string instruments. In this paper,we studied the standing waves on the metallic string and gave two methods on the measurement of standing wavelength using the new experimental instrument. One was based on the formula of standing wave and the other was directly observing standing waves to get the wavelength. Through a lot of data processing and analysis,we compared these two methods and gave definite reference for determining and improving the experimental instrument.