Because of quite a certain content of alkali metal in biomass, bed material agglomeration appears in the process of thermal reaction in fluidized bed, which can destroy fluidization. In the paper, fluidized bed gasification experiments on alkali metal enrichment were made, of which cotton straw pellets were used as fuel. The results are shown that experiments could keep running by bed material replaced at regular time without slag and the component of the bed material maintained stability. The replaced bed material could be used again after being washed. Through the XRF analysis, it could be found that the potassium compound with high dissolubility could be removed by washing.