Two kinds of bed materials were used as bed materials when a biomass of cotton stalk was burnt in a circulation fluidized bed (CFB) combustion pilot plant (0.2 MW). After a long time operation, silica bed materials were found sintered while aluminous bed materials slightly changed. The particles of both kinds of bed materials were sampled and three instrumental approaches were performed (XRF, SEM/EDS, XRD) to identify the bed materials in order to find out the mechanics of agglomeration. The result shows that both of the bed materials were enriched with alkali metals but the changing speed of enrichment of aluminous particles was much slower than that of silica particles. The CFB could go steadily and well at least 72 h under our experimental condition when aluminous particles were used as bed material. Agglomeration of aluminous bed materials was reduced due to the protective element aluminous.