Abstract: Trace oxygen elements in CaF₂ crystal, YF₃ thin films and Au thin films were tested using time of flight secondary ion mass spectrometry. The results show that by changing the size of the analytical ion source aperture to change the ion beam current, the unit area ion dose acting on the sample surface was changed. As the ion beam current increased, the fluoride and oxygen ion yields of CaF₂ crystal and YF₃ film both increased, indicating the presence of oxygen in CaF₂ crystal and YF₃ film. The test results were consistent with the UV spectrum test results of CaF₂ and the infrared spectrum test results of YF₃ film. When the ion beam current increased, the Au ion yield increased, while the oxygen ion yield showed no significant change, indicating that the detected oxygen element came from residual gas in the experimental environment, and there was no oxygen element present in the Au film.