Established an UPLC method in determination the amino acids of dairy products, and detected the amino acid content of dairy products processed in different temperature, to identify the spray dried milk through the changes of amino acids contents and composition. The results showed that the calibration curve was linear in the range of 0.003 7～0.052 2 mg/mL of amino acids, the average recovery range of amino acid was from 97.45%～105.65%. It has the advantage of simple, rapid and accuracy in the determination amino acids. With the spray temperature changing, the content of amino acids were different. And the change of Glu, Leu, Cys were the most obvious. It can serve as the distinguish method of reconstituted milk.