Abstract: Based on reviewing the structure and principle of the quadrupole linear ion trap, this review explains the core technical principles of the linear ion trap electronic system and cascade mass spectrometry, and introduces the stored waveform inverse Fourier transform technique in quadrupole linear ions. The application in the well, especially how to select the parent ion. The quadrupole linear ion trap is a magical analyzer that analyzes ions with a mass-to-charge ratio of thousands or more. In the full scan mode, the ion trap still has high sensitivity, and its sensitivity is often 10-1 000 times higher than that of the quadrupole. Compared to other types of analyzers, MSⁿ of multi-stage tandem mass spectrometry can be achieved with a single linear ion trap, which is very useful for structural identification of analytes. The resonance-assisted alternating voltage is used to excite the parent ion and the fragment ion, which is the key to achieving cascade mass spectrometry. In addition, the quadrupole linear ion trap is relatively easy to manufacture, requires low processing accuracy, and is cost effective. This review will introduce the mechanical structure of the quadrupole linear ion trap and the technical principles of circuit implementation; describe how to apply collision induced dissociation and assisted RF to achieve linear ion trap tandem mass spectrometry; explain how to pass RF voltage and DC voltage in a linear ion trap. The cooperation is to capture and excite ions; finally, the practical application of the stored waveform inverse Fourier transform technique in selecting parent ions and separating adjacent mass ions is also demonstrated.