The oxygen vacancy and mobile ions play major role on the resistance switching in a typical RRAM by the modulation of filament conduction. It is also known that soft-breakdown played a major role on the switching mechanism. However, the understanding of the mechanism involved in the soft-breakdown is not clear enough. In this paper, we demonstrated a pulsed RTN transient measurement technique which enables the determination of trap generation and its evolution with time. On the demonstrated sample with a HfON/Al2O3 MIM structure, different operations will generate different traps which can be revealed from the trap profiling. The soft-breakdown path can then be delineated for forming, SET/RESET processes. The results show that the path behaves like a cone, widening at the bottom electrode and narrowing on the top, with a neck and waist near 2 electrodes, which can properly describe the RRAM operations.