Cusped field thruster is a new kind of thruster which confines plasma by magnetic mirror effect to produce thrust. It is characterized by long lifespan and adjustable thrust in a large range, which makes it have great potential applications in drag free satellites and commercial space satellites. It was put forward first by THALES Electron Devices in Germany and sponsored from European Space Agency. There are several institutions are engaged in the research of this thruster, including Massachusetts Institute of Technology, Stanford University and Technische Universiteit Delft. Now the test experiments on the cusped field thruster using Xe, Kr and Ar are being carried out in the laboratory of plasma propulsion of Harbin Institute of Technology to ascertain the ionization regulations of different propellants under the high voltage and strong magnetic field conditions. On this basis, it is significant to know the mechanism about how the performances change with propellant and provide the foundation for the cusped field thruster using different propellants. In this paper, the principle and design process of this thruster are presented. Then it can be found that the thruster can be ignited easily by using Xe compared with by using Kr and Ar under the same volume flux, which is caused by their differences in ionization energy and ionization section. Experiments show that the cusped field thruster can be ignited under 200 V while it cannot be ignited by using Kr and Ar even under 1000 V under the same volume flux. Then the performances of cusped field thruster using three propellants are tested. It can be found that there are obvious differences in anode current, thrust, efficiency and impulse using three propellants under the same conditions. The diagnosing of plume using Faraday probe shows that the propellant utilization causes the difference in performance which is related to ionization process. The experiments show that the utilization rate of Xe is over 90 percent, while the utilization rate of Kr is less than 60 percent and the utilization rate of Ar is less than 20 percent. The obvious difference in ionization voltage can reflect the difference in performance. The experimental results under the same flux show that the utilization rates of Kr and Ar can be improved by increasing flow density and reducing the collision free path between atoms. Experiments show that the peak utilization rate of Ar can be improved to 50 percent approximately. In the aspect of plume structure, the results of Faraday probe show that the hollow plume can be observed and the angle linked with peak ion current density decreases with atom mass decreasing.