Abstract: As an important protection device in the DC power system, the bypass switch usually works under open circuit conditions. In order to analyze the insulation reliability of the vacuum bypass switch, a three-dimensional physical mathematical model of the electric field is established by using the finite element method to illustrate the distribution of the electric field under standard lightning impulse to withstand peak voltage. The macroscopic enhancement factor of surface electric field intensity is introduced to quantitatively describe the uniformity of the electric field concentration region. Moreover, the chaotic polynomial expansion method is applied to analyze the uncertainty of the center slot fillet radius of the contact electrode to ensure the reliability of insulation performance and manufacturing processes.