The floor area of a vertical grounding electrode is much smaller than that of a conventional horizontal grounding electrode, which is an effective way to solve the difficulty of site-selecting of DC grounding electrodes. The vertical grounding electrode of Pu’er is the first vertical grounding electrode of UHVDC in China. Starting from the problem of uneven distribution of inner and outer electrodes of Pu’er electrode, it is found that the shielding effect of the inner electrode is higher than that of the outer electrode, and the idea of unequal parameter design for inner and outer electrodes is put forward. Then, based on the boundary element simulation software, it is found that changing the length of the electrode can make the shunting of the inner and outer electrodes more uniform, the influences of the length and number of electrodes on the length matching of inner and outer electrodes are studied. The fitting formula for the optimum length of the outer electrode is given, and an algorithm for optimal length of outer electrodes for horizontal layered soil structures is proposed. Finally, a typical double circular vertical grounding electrode optimization design case is used to verify the feasibility of the algorithm.