The invention relates to a mass spectrometer, a mass spectrometry method and a detection system. The mass spectrometer includes a vacuum chamber having a working pressure being 0.1 Pa≤P≤10 Pa; a linear ion trap, arranged in the vacuum chamber, wherein a field radius r of the linear ion trap is r≤5 mm; and a power supply, configured to provide a radio-frequency voltage for the linear ion trap, a frequency f of the radio-frequency voltage being 2 MHz≤f≤10 MHz. Because a vacuum level is relatively low, this vacuum condition may be realized by selecting a roughing pump for evacuating; and compared with a combined pump unit which is generally selected by a traditional mass spectrometer using the linear ion trap and is composed of a turbo molecular pump and a roughing pump, the roughing pump has a lower pumping speed, smaller size and lower manufacturing cost.