This study was based on the thiol groups(-SH) of PC2～PC6, which could be reacted with the Monobromobimane(mBBr), in order to get polypeptide derivatives with fluorescent signal. A new method was developed for measuring the Polypeptides by high performance liquid chromatography with fluorescence detector, then the chromatographic conditions of HPLC was optimized;meawhile the reaction proportion of PCs and mBBr was identified by Trap-MS. The results showed that, the reaction proportion of PCs and mBBr was 1∶1, the polypeptide derivatives had good stability;the five compounds separation was better, and the peak time focused on the 16.6～22.0 min;the linear correlation coefficient of PC2, PC3, PC4, PC5 and PC6 was >0.999 1, and the limits of quantification were 0.3, 0.05, 0.3, 0.5 and 0.8 mg·L-1 respectively, the recovery rate was 83.0%～102.0%;the method was reproducible, RSD<2%, this method for measuring the peptide compounds was rapid and accurate.