Abstract: The influence of the emitter’s geometric parameters on the performance of the ionic liquid thruster is studied, based on a PIC (particle-in-cell) simulation model of a single emitter. The beam distributions, as well as the curves of the thrust and specific impulse are obtained. Then, the simulated curves of the average thrust and the angular efficiency of a single emitter are obtained by adjusting the electrode spacing and the extractor aperture, to analyze the influence of the emitter on the performance of the thruster. The following conclusions are drawn: before the ions are intercepted by the extractor, the angular efficiency of the thruster is directly proportional to the electrode spacing and inversely proportional to the extractor aperture; without considering the change of the number and the fraction of the emitted ions, the thrust of the thruster increases firstly and then decreases with the increase of the electrode spacing, and increases with the decrease of the extractor aperture within a certain range. However, a very small extractor aperture will cause a significant thrust loss and the electrode erosion. The above results may serve as a reference for the optimal design of ionic liquid thrusters.