In order to improve the utilization efficiency of the circulating fluidized bed boiler (CFB) ashes on engineering, two sets of experiments which use jet mill to make CFB ashes ultra-fine are conducted with the help of different frequency of classifier. Through these experiments, the ultra fine CFB ashes of different size distributions are attained which are d50=9.07 mu m and d50 = 6.49 mu m respectively and the compressive strength test of concrete mixed with ashes are conducted on hydraulic universal testing machine. The results reveal that the compressive strength of concrete mixed with ultra-fine CFB ashes is higher than that of concrete with no ash content, and it rises from 96.33KN to 105.33KN with decreasing particle size of CFB ashes. Test results show that the utilization of CFB ashes is feasible by processing ultra-fine CFB ashes.