Abstract: Microstructure evolution of coarse particles in fluidized bed combustion (FBC) was investigated by SEM technology, diagram processing technology and physical absorption method. It was found that the quantity of micro-pores increased when their sizes were less than 400 pixels in diagram for bituminous coal, but never changed when their sizes were larger than 400 pixels. The specific surface area of coarse particles obviously increased with increasing combustion time during fluidized bed combustion.