Abstract: China Institute of Atomic Energy (CIAE) is preparing to develop a 2×6 MV tandem accelerator. In the initial stage of development, the dimensions of the high voltage electrode and the potential distribution ring need to be designed and calculated according to the requirements, so as to facilitate the design of the grounded enclosure and the arrangement of the components in the later stage. In order to obtain the dimensions of the high voltage electrode and the potential distribution ring, the electromagnetic field simulation software was used to build the two dimensional model of the tandem accelerator and calculate its electric field intensity distribution in this paper. In view of the influencing factors such as the structure of the high voltage electrode, the cross sectional shape of the potential distribution ring and the ring spacing, measures to optimize the size were proposed by comparing the electric field intensity distribution of the tandem accelerator. The simulation results show that the high voltage electrode has a cylindrical structure, and there is the electric field distortion at the border with the potential distribution ring. The maximum electric field intensity on the surface of the component is 69.7% higher than that of the surface electric field intensity at the center of the high voltage electrode, which is prone to breakdown and sparking. The high voltage electrode has a circular arc transition structure which makes it have a shielding effect, and effectively reduces the electric field intensity on the surface of the high voltage electrode and the potential distribution ring near it. And after data analysis, it is found that the peak value of the electric field on the surface of the high voltage electrode decreases with the increase of k, and the peak value of the electric field on the surface of the potential distribution ring increases slowly with the increase of k. If only modifying the shape of the high voltage electrode can only reduce the surface electric field intensity of several potential distribution rings close to it, it cannot solve the electric field distortion caused by the gap between the potential distribution rings. Making the cross sectional shape of the potential distribution ring an ellipse and reducing the ring spacing can improve the influence of electric field distortion on the surface electric field of the potential distribution ring. According to the electric field intensity distribution on the component surface, it can be seen that the method of reducing the ring spacing has a greater contribution to reducing the electric field intensity on the surface of the potential distribution ring. Finally, the maximum outer radius of the high voltage electrode is 686 mm, the minimum outer radius is 586 mm, the length is 1 314 mm, the long axis of the arc is 45 mm, and the short axis is 22 5 mm. The potential distribution ring uses an elliptical cross section, the long axis of the ellipse is 90 mm, the short axis is 45 mm, and the ring spacing is 16 mm. The dimensions of the optimized high voltage electrode and potential distribution ring can meet the requirements of the newly developed tandem accelerator.