The fluidized bed combustion of rice straw was investigated in a lab-scale reactor. The influence of fluidization velocity and bed temperature on the fluidization time was investigated. The effect of regulating running parameters on the fluidization recovery after the defluidization had occurred was studied. Experimental results showed that the fluidization time decrease with the increase of the bed temperature or decrease of the fluidization velocity. Fluidization can be recovered only by means of decreasing the bed temperature. The SEM/EDS analysis results showed that the molten materials in the agglomerates are formed by the burning fuel particles. At last a new agglomeration mechanism was proposed. The results are helpful for the design and operation of biomass-fired fluidized bed and further understanding of the agglomeration mechanism.