A closed multi-room fluidized bed sludge drying method is provided, which is a sludge drying method having the advantages of simple equipment structure, convenient operation, strong sludge adaptability, high thermal efficiency, safety, continuity, stability, etc. After the mechanically dewatered sludge is mixed with the back-mixed sludge, the mixture is dried room by room in an inert particles multi-room fluidized bed dryer (3). The first room and the second room of the inert particles multi-room fluidized bed dryer (3) adopt inert particles (f) as heat storage medium. Gas from a cyclone separator (5) goes through a spray tower (7) and returns into an air heating unit (4) through a circulating fan (10). Part of dried sludge (e) at the lower part of the cyclone separator (5) enters the inert particles multi-room fluidized bed dryer (3) through the back-mixing in a mixer (2). Waste liquid from the bottom of the spray tower (7) enters a waste liquid circulating pool (8), with part of waste liquid circulating into the spray tower (7) and part into a sewage treatment system.