I will talk about our studies on various graphene-based moiré materials. I will show that band topology and electron interaction can be easily tuned by electric field in these systems, which opens the door for various fascinating quantum many-body phenomena. For topologically non-trivial active bands, quantum anomalous Hall insulator can emerge. For topologically trivial active bands, there can still be intriguing phases such as spin liquids and orthogonal metals due to electron-electron interaction. I will also talk about the effect of quasi-periodicity due to the hBN substrate. The alignment angle between hBN substrate and twisted bilayer graphene strongly affects the low energy density of states and conductivity.