Abstract: Numerical study on the sensitivity of the ionization gauge is critical for predicting and optimizing its performance.A discretization method based on the discrete electron trajectory fragments to accurately calculate theoretical sensitivity is proposed in this paper.The fundamental theoretical model of the ionization gauge operation process considering boundary condition variation is expressed as a time linear electronic trajectory composed of many discrete segments.In each tiny time interval,the discrete effective electron trajectory fragments are calculated and screened by constructing the effective ionization space,and the ionization cross section is calculated with the help of Binary-Encounter-Bethe model.Then the ionization gauge sensitivity is solved using the discretization method to a small error of collection efficiency and ionization cross section.The effectiveness of the method is demonstrated by the results of hot-cathode and cold-cathode ionization gauges experimentally and theoretically.The theoretical results are in good agreement with the experiments.The simulation deviation is below 5.6%,4.5%for cold cathode and hot cathode ionization gauge,respectively.