Abstract: The principle and performance of a home-made miniature photoionization ion trap mass spectrometer was introduced. The ultraviolet photons with the energy of 10.6 eV were generated by VUV lamp, and they were irradiated into the ion trap. The volatile sample in the ion trap was ionized by the photons, and then captured and analyzed by the ion trap. The ion trap was not only used as ionization volume, but also mass analyzer, which continually collected sample ions in order to enormously improve the detection sensitivity of mass spectrometer. Photoionization is a soft ionization method. Therefore, there’re only single charged parent ions of the sample gas molecule under the condition of photons’ irradiation effect, and no fragment ions produced. Consequently, the mass spectra obtained from photoionization is very simple, and the sample gas can be detected without preseparation. The integration of soft photoionization and ion trap mass spectrometer is specially fit for in-suit detection of VOCs and noxious gas. Thus, there will be a far-ranging market prospect.