Abstract: A method of particle simulation based on unstructured mesh is proposed in this paper to reveal the basic characteristics of ion thruster's plume with complex spacecraft configurations. The method of grid discretization and the topological relationship among the generation of grids are discussed. An algorithm of particle motion is developed to push the particles in grids, then the method of matrix permutation based on the RCM algorithm is used to reduce the bandwidth of the matrix. Finally, a simulation example is compared with experiment results to validate this method.