Using the diffusion limited aggregation model in Cartesian grid，equilateral triangle mesh and hexagonal mesh，we simulate the tree fractal structures. For avoiding the impact of the direction of the movement，we simulate the metal ball movement in the electro fields to generate the fractal structures. The results of fractal dimensions of different charge densities are obtained by using the Sandbox method. The fractal dimension decreases when the charge density increases. It confirms to the experimental result