The short-timescale variability of tidal disruption events (TDEs) and changing-look active galactic nuclei (AGN) provides an ideal laboratory for studying the evolution of black hole accretion disks and coronae. We developed a black hole accretion disk-corona model, and the disk-corona evolution is derived by fitting the multi-epoch X-ray spectra of TDEs. Its evolutionary characteristics are similar to AGNs, which may help understand the physics of the accretion disk corona surrounding supermassive black holes. When a CLAGN is in its low state, a hot accretion flow (similar to a hot corona) surrounds its central black hole. The hot accretion flow is suppressed to a cold accretion disk in the high state of the CLAGN. We studied the cooling process of the hot accretion flow to form a cold accretion disk, and found that the timescale of accretion mode transition ranges from several years to decades, which is consistent with the observations. We pointed out that this mechanism provides a new approach to solving the short-timescale variability problem of CLAGNs.
