The characteristics and mechanism of set/reset process in high-k based resistive random-access memory devices were studied. A great fluctuation in set/reset voltages was observed in the NbAlO single-layer RRAM devices. However, it shows highly uniform and reproducible switching cycles in Al2O3/NbAlO/Al2O3 nanolaminate stack structures. Based on the electric-filed modulating effect, we proposed a unified resistive switching model to simulate the set and reset operations, and the switch parameters dispersion due to the great randomness of the conductive spots formation or annihilation was discussed for a single-layer RRAM. When an ultra-thin Al2O3 films was embedded in NbAlO-based RRAM devices, there is an obvious improvement in the stabilization of the set/reset switching voltages. It can be explained that the electric-field distribution is rearranged and locally controlled in the stack structure, therefore the conductive filament bridges and ruptures appear in the thin buffer layer.