Abstract: The insulation performance of oil paper insulation, as the main insulation form of power transformer, is closely related to the moisture content. Accurately obtaining the moisture content of oil paper insulation is crucial for transformer fault early warning. Driven by the gradient of multiple physical fields such as electric field and temperature field inside the oil immersed transformer, the moisture is always in the process of dynamic migration, and the spatiotemporal distribution is complex, which is difficult to measure directly. Therefore, it is necessary to study the characteristics of moisture migration. This paper summarizes the research results on the mechanism, model and characteristics of moisture migration in oil paper insulation as follows: moisture migration is a process of interaction between water molecules in different forms and the microstructure of insulating oil paper, which is significantly affected by multiple physical fields. The existing research on moisture migration in oil paper insulation is mostly based on the Fick's law. The diffusion coefficient is used to characterize the influence of moisture gradient and temperature on moisture diffusion velocity, whereas they failed to deeply couple multiple physical fields, and the uneven distribution characteristics of moisture under the temperature gradient can not be obtained. The change law of diffusion coefficient and corresponding moisture migration process under the multiple factors such as material properties, temperature and electric field are obtained. However, the way of coupling influencing factors to diffusion coefficient can not accurately describe the influences of multi-physical fields on moisture migration characteristics, and there is a lack of research on moisture migration law under the electric field. The heat moisture coupling model based on the principle of driving potential balance can describe the spatiotemporal distribution of moisture and quantify the influence of electric field on the dynamic migration of moisture. It is necessary to further carry out the experimental research based on the nondestructive measurement of moisture spatiotemporal distribution, deepen the modeling of moisture migration under the coupling of multi-physical fields, and build a theoretical system under multi-physical fields, so as to accurately characterize the spatiotemporal distribution of moisture migration of oil paper insulation in oil immersed transformer.