Abstract: Oxidant performic acid was prepared by formic acid and hydrogen peroxide, cystine and methionine were oxidated into sulfo alanine and methionine sulfone by formic acid, respectively, and then derivatived with PITC. The products were separated on a XB-C18 (4.6 mm×250 mm, 5 μm) by using gradient elution with acetonitrile-water (80/20, v/v) as mobile phase A and 50mM sodium acetate buffer solution (pH=6.5)-acetonitrile (93/7, v/v) as mobile B, and real samples were detected at 254 nm with column temperature of 40℃. The results showed that derivation products were stable,whose relative standard deviation (n=6) of peak area were 1.81%, 1.65%, respectively,and had good linear correlation between 187.5~1500 μg/mL, whose average recovery met requirement of the experiment.