Abstract: The mass resolution of the ordinary ion trap mass spectrometer derived from the quadrupole mass spectrometer usually ranges from hundreds to thousands. In this study, the fine secular frequency resonance oscillation was observed with a rectilinear ion trap mass spectrometer. The FWHM of the responding resonance secular frequency of benzene was 0.012 kHz. The corresponding mass resolution was 8600 m/Δm for benzene (m/z=78). The mass spectrometer with secular frequency scanning has a linear response to benzene in the concentration range from 200 ppbv to 10000 ppbv. This study shows a new feature of the secular frequency scanning for ion trap mass spectrometers.