Abstract: Dielectric polymer nanocomposites possess excellent electrical, thermal and mechanical properties, and are widely utilized in power- and energy-related fields. The special properties of dielectric polymer nanocomposites are attributed to the interface formed between the polymer matrix and the nanoparticles. However, conventional analyzing methods cannot provide direct evidence of the interacting mechanism of the interface. The in-situ testing of the interfacial region based on atomic force microscopy (AFM) has thus become an important research direction. This paper provided a review on the recent research progress of the in-situ AFM study of interfacial region in dielectric polymer nanocomposites. First, the working principle of AFM was briefly introduced. Then, the AFM studies on dielectric and polarization properties, charge distribution and transport, and microregion structure were presented. Finally, problems existing in the in-situ AFM testing of interface in dielectric polymer nanocomposites and future development direction of the interface study were discussed.