MOCVD is a reliable method to deposite a epitaxial thin film on a large sized or arbitrary shaped substrate. But OM precursors contain organic ligand,, that is to say, many carbons. It is a very important problem how carbons of organic ligand react with oxidation source in gas phase and growing surface of thin film. In this experiment a superconducting thin film of $Y_{1}Ba_{2}Cu_{3}O_{7-x}$ is deposited by MOCVD on MgO polycrystal at Ts=780℃. The thin film is in-situ analysed by XPS.