Volatile threshold switching (TS) and nonvolatile memory switching (MS) are two typical resistance switching (RS) phenomena in oxides, which could form the basis for memory, analog circuits and neuromorphic applications. Interestingly, TS and MS can be coexistent and converted in a single device under the suitable external excitation. However, the origin of the transition from TS to MS is still unclear due to the lack of direct experimental evidences. Here, we directly observe the conversion bet