In the string vibration experiment, the string length is changed on the premise that the tensionapplied at the fixed end is unchanged.Using the relationship between vibration frequency and standing wavewavelength ,the linear density of string is obtained.By comparing the results of string linear density and stringmass length ratio under different chord lengths, the influence of chord length on the measurement results ofstring linear density is discussed ,and the necessity of reasonable selection of chord length in string vibrationexperiment is analyzed.