Abstract: The physical and chemical properites of flying coal ashes and the releasing patterns of silicon were studied．The results show that the flying coa l ashes can be used as soil modifier because the physical sand accounts for 44.43％～98.67％ in the ashes and their volume weights are lower than those of soil and their pHs generally excess 7.5．The difference in contents of water-soluble and available silicon between the ashes and soil is not obvious，but the amount of silicon released from the ashes in 100 hours is 3．0～25．0 times as high as that in soil，so the ashes can supply the growth of rice with Si．The releasing processes of Si in the ashes and soils can be well described with Elovich equation and Freundlich equation，in which the parameters，b value and k value，can express the releasing capacity of silicon in the ashes and soils．The larger of b and k，the more silicon is released．