Abstract: Electrodeless Lorentz Thruster (ELF) has the characteristics of high specific impulse, electrodeless corrosion sputtering, large thrust, and a wide selection range of working substances. It can also be considered to combine with other thrusters to form a composite thruster and can be the development direction of the new high-power thruster. This paper presents a circuit model for the thruster. The rotating magnetic field coil is equivalent to a lumped parameter inductance with a phase difference of 90°. The plasma is modeled as an inductive load with capacitive and resistive elements. Based on Kirchhoff's law and the current continuity equation, a series of equations are derived. The plasma is accelerated under the action of Lorentz force. The results show that for high input energy, the efficiency is inversely proportional to the input energy, the specific impulse and efficiency increase with the increase of coupling, and there is an optimal efficiency with the increase of input energy.