Based on the incremental regularity of γ-(Glu-Cys)n-Gly series compouds,the qualitative and quantitative analyses of peptides were achieved by using Trap-MS ion screening function.The thiol groups(—SH) of PC2-PC6 could react with the monobromobimane(mBBr) to get polypeptide derivatives with fluorescent signal,and the reaction proportion of PCs and mBBr was 1∶1 identified by Trap-MS,which also showed that the intensity of the polypeptide derivatives was stable in 1 week.HPLC-Trap-MS and the chromatographic conditions of HPLC were optimized.The ion extraction results showed that the method was rapid and accurate,and the compound separation effect was obvious,PC2,PC3,PC4,PC5 and PC6 had wide linear ranges with linear correlation coefficients more than 0.999,and the detection limits were 0.13,0.02,0.17,0.39,0.82 mg/L,respectively.The recoveries were in the range of 89.0%-99.5%,and the method was reproducible with RSDs less than 3.5%.The quantitative analysis under the double detectors of the fluorescence and the mass spectrum could be realized by the fluorescence labeling and Trap-MS screening of peptide compound,which could be used to analyse polypeptide compounds rapidly and accurately.The content of polypeptide in alga was detected after being induced by Zn and Cd,and the results showed that the polypeptide had an induced response to the metal,in which the small molecular peptide changed obviously,the induced response of peptide to the heavy metal was delayed with the increase of the carbon chain.