The invention relates to a mass spectrum analyzer and particularly relates to a VUV lamp ionization source device for the continuous on-line monitoring of mass spectrometry. The specific structure ofthe device comprises a VUV lamp, an ionization source chamber, a baffle valve, a vacuum gauge and a vacuum pump. A sample molecular sample injection tube, an electrode group, a polytetrafluoroethyleneinsulated ring group and a Skimmer electrode are arranged in the emission direction of the VUV lamp in the ionization source chamber, all electrodes are flat plate structures with intermediate circular holes and are parallelly and coaxially placed in an insulating way. According to the ionization source device, with a low-pressure charge transfer reaction as a mechanism, the ultraviolet light generated by the VUV lamp collide sample molecules to cause a charge transfer reaction and the sample molecules are separated. According to the new ionization source device technology, the efficiency ofthe continuous online ionization of materials which are difficult to ionize by the VUV lamp is improved greatly, and the device has broad application prospects in the fields of environmental monitoring, food safety, medical diagnosis and the like.