Abstract: The analytical sensitivity is the main performance indicator of the thermal ionization mass spectrometer(TIMS). There exist many factors which lead to sensitivity deterioration of the spectrometer with using it year by year. Sometimes, it is actually difficult to find out the exact reason and figure the deterioration out. On the basis of the fundamental of the positive thermal ionization mass spectrometer(PTIMS), this paper summarized several main factors influencing on the analytical sensitivity, such as, materials of metal band, filament configuration, sample loading and high vacuum condition. This paper described the above factors how to affect the analytical sensitivity in detail and proposed several rational solutions. At the end of each section, maintenance suggestions for the spectrometer were putted forward.