Chemical looping combustion technology can effectively decrease the pollutant emissions from the dried sewage sludge incineration. The mixing and separation of binary mixtures of dried sludge and iron-based oxygen carrier are involved in the fluidized bed due to their big difference in physical properties. The fluidization experiments of binary mixtures of dried sewage sludge and iron-based oxygen carrier were carried out in a plexiglass cold fluidized bed with 100 mm inner diameter in this study. The effects of particle size, mass ratio of dried sewage sludge and oxygen carrier and operating velocity on the fluidization characteristics were investigated. The results showed that the sludge can be mixed well with the oxygen carrier with mean particle size of 0.66 mm, and the minimum fluidization velocity ( ) was equal to the minimum mixing operation velocity (Um). When the mean particle size of oxygen carrier was 1.46 mm, it gradually transited from the separated fluidization state to the mixed fluidization state as the operating velocity increased, and the Um was greater than in this condition. When the mean particle size of oxygen carrier was 2.43 mm, the separated fluidization state was always maintained. Based on a proposed dimensionless number Gd for judging the mixed/separated fluidization state of binary mixtures of dried sewage sludge and iron-based oxygen carrier, the binary mixtures were in a mixed fluidization state while 0<Gd<0.8, and the binary mixtures were in a separated fluidization state while Gd>0.8.