The distinguishing criterion of unstable defluidization and stable defluidization is to observewhether partial defluidization occurs at the beginning of fluidization, which can be identified by the occurrence of a ‘V’ type change of the pressure drop in the initial 10min or by the visual observation. It should be noted that such distinguishing criterion will bring some error (about 0.15 wt.%) on the critical carbon content value of distinguishing different fluidization behavior, which is acceptable.