Abstract: The magnetic field simulation and design is very important for improving the performance of the Helicon Plasma Thruster(HPT). The magnetic field configuration is closely related with the processes of the propellant's ionization, acceleration, exhaust and the electrical plume contamination control. Based on the equivalent magnetic charge method, a three dimensional magnetic model is built for the HPT system. The magnetic field configuration and the field intensity distribution are computed for the assembly of cylinders and annular Nd-Fe-B permanent magnets. The feasible magnetic shape is chosen from a large number of magnetic field simulation results, which may help the development of the HPT system and be used to reduce its cost.