Advanced transmission electron microscopy combined with in situ techniques provides powerful ability to characterize the dynamic behaviors of phase transitions, composition changes and potential variations in the nanomaterials and devices under external electric field. In this paper, we review some important progress, in this field, of the explanation of structural transition path caused by the Joule heating in C60 nanowhikers, the clarification of electron storage position in charge trapping memory and the direct evidences of the oxygen vacancy channel and the conductive filament formation in resistive random access memory. These studies could improve an understanding of the basic mechanism of nanomaterial and device performance, and also demonstrate the diversity of the functions of transmission electron microscopy in microelectronic field.