Hexagonal boron nitride (hBN), which is a 2D layered dielectric material, sometimes referred as white graphene due to its structural similarity with graphene, has attracted much attention due to its fascinating physical properties. Here, for the first time the use of chemical vapor deposition -grown hBN films to fabricate ultrathin (approximate to 3 nm) flexible hBN-based resistive switching memory device is reported, and the switching mechanism through conductive atomic force microscopy and ex situ transmission electron microscopy is studied. The hBN-based resistive memory exhibits reproducible switching endurance, long retention time, and the capability to operate under extreme bending conditions. Contrary to the conventional electrochemical metallization theory, the conductive filament is found to commence its growth from the anode to cathode. This work provides an important step for broadening and deepening the understanding on the switching mechanism in filament-based resistive memories and propels the 2D material application in the resistive memory in future computing systems.