Abstract: Linear ion trap (LIT) comprised of four electrodes has been widely used in recent years. Because of the symmetry of the electrodes, the electric field in the LIT is symmetrical in the axial direction. As a result, about 50% of the trapped ions are ejected from one of a pair of electrodes in the process of mass analysis, which can be detected for one detector. In this study, a DC offset was applied to the electrode on the opposite side of the detector, which shifted the positive ions towards the electrode on the side of the detector. This helped the trapped ions to eject unidirectionally. And over 50% of the trapped ions could be detected. Four ions of different mass-to-charge ratios were investigated in this experiment. The results show that the positive DC voltage in a certain range increases the ion intensity. The increments of the ions are 20%，38%，31%，44%， respectively. This method is simple in principle, convenient in experimental technique.