The present disclosure relates to a method for detecting DTPA content in ADC by LC-MS/MS. The samples are derivatized with Fe3+ under a weak alkaline derivatization condition, and a weak alkaline mobile phase is used, without need for addition of ion-pair reagents. This method has the characteristics of high efficiency, high stability and strong durability, and can well make up for the defects of few DTPA detection methods and complicated operations in the prior art.