Using deionized water as the cooling medium, the cooling system of phase-change valve faces challenges in balancing insulation and heat dissipation performance,which affects the reliable operation of the system.Leveraging superior heat dissipation capabilities, phase-change cooling techniques are being gradually applied for cooling high-voltage high-power power electronic devices.However, bubbles in the liquid dielectric pose risks of insulation degradation.To better understand the migration characteristics and insulation characteristics of bubbles in the extremely inhomogeneous electric field associated with phase-change cooling, numerical simulation methods are applied to analyze the effects of three key factors on the trajectory of bubble motion,which are bubble diameter, velocity and electric field strength. Furthermore, after entering low field strength regions, the impact of bubbles with different contact angles, on the electric field distribution over insulator surfaces has been studied.The results reveal significant effects of various factors on bubble motion trajectories, provide an improved understanding of bubble migration and insulation characteristics in phase-change,and hold important reference value for the further application of phase-change cooling in DC equipment.