The migration process of space charges in liquid dielectrics under a strong electric field often includes complex dynamic processes such as charge generation, scattering, and disappearance, which are difficult to measure. In this paper, SiO₂ films with thickness of about 100, 200 and 400 nm are deposited on the electrode surface by magnetron sputtering, respectively. To explore the effect of space charge injection on its subsequent migration at switching overvoltage, the electric field and space charge distribution are measured based on the Kerr electro-optic effect, and on the basis of that, the film thickness effect on the charge migration of propylene carbonate is discussed. The results show that, the increase in film thickness effectively suppresses the amount of charge injected by the electrode, compared with the case where the SiO₂ film is not deposited, but it has little effect on the space charge mobility of the liquid dielectric. A measurement method for measuring the space charge mobility of liquid dielectric is proposed, which is used in the simulation of space charge transport process in the future work.