In order to optimize the optical component cleaning process,the oxygen dissociation by synchrotron radiation has been researched by analyzing the gas composition produced in cleaning process.The gas composition is measured by quadrupole mass spectra when synchrotron radiation light irradiates the oxygen filled in vacuum chamber.The gas composition and content can be established by analyzing the data gathered.Experimental results indicate that oxygen can be dissociated by synchrotron radiation light to produce some species with strong oxygenation,such as oxygen atom and ozone.The content of oxygen atom is about 1% and the content of ozone is about 0.005%～0.01% in cleaning process.