Some properties of standing waves on strings were demonstrated using Guitar and smartphone. The influence of tension and line density on the fundamental frequency of standing waves on strings can bequalitatively demonstrated.Then the frequency relationship between the fundamental frequeney of the standingwave and higher-order harmonics , as well as the relationship between the fundamental frequency of the standingwave and the string length were quantitatively demonstrated. The results of the quantitative demonstration are ingood agreement with the theory of standing waves on strings. The use of Guitar and smartphone for the standing wave demonstrations provides students with an auditory extension to understand the properties of standingwaves ,and adds fun to traditional experimental teaching.