Abstract: Purity measurement of the peptide is the key to building metrological traceability for the measurement value of peptides in clinical chemistry, pharmaceutical chemistry, food chemistry, and other fields. In addition to the mass balance method, nuclear magnetic resonance method, and hydrolysis method, organic elemental analysis is a new technique for measuring the purity of peptides in chemical metrology. However, a detailed introduction to this technique is yet to be reported. In this paper, a technique for peptide purity measurement based on the analysis of nitrogen, sulfur, and other elements has been established. Using oxytocin as a typical sample, the nitrogen and sulfur elements in the sample were analyzed, the content of nitrogen and sulfur elements in the main component was obtained by deducting the content of nitrogen and sulfur elements in the relevant structural impurities, and the purity results of the peptide were obtained by calculation using the information of the number of atoms and molecular weight of nitrogen and sulfur elements in the molecule of the peptide. The relative standard deviation was less than 1% compared with the measurement results of the authoritative mass balance method. The results of the impurity-corrected organic elemental analysis technique established in this paper are accurate and reliable and can be used for peptide purity standard substance determination.