Abstract: Based on the Coulomb’s law and the current continuity equation, this paper solutes the electric field of the charged particles group at a certain point in space, and considers a series of reasonable approximation. The two-dimensional space-charge-limited flow first-level approximating formula in the axial symmetry column conductor is obtained. The result reveals that for a limited plane the computed charge-limited flow by the two-dimensional is bigger than that by the classical one dimension formula.