Change-Look AGN (CLAGNs) shown with disappear/re-appear of broad lines or strong variation of X-ray absorption in a couple of years have challenged the AGN unification model. The physical mechanism for changing look is still unclear. I will review the observational properties of CLAGNs (e.g. evolution of spectral energy distribution, variability in multiwavebands, etc.). We propose that most of CLAGNs may be caused by the change of radiative efficiency at Eddington ratio ~1%, where the accretion modes have changed. The CLAGNs stay in a transitional stage of galaxies, which transit from AGNs to quiescent stage or vice versa.