Abstract: The fly ash, firepower plant offal, is composed by amorphous glass sphericity grains, whose sizes are different and whose structures are loose. Its main chemical element is aluminosilicate. Under the hydrothermal condition, Holler and Wirsching synthesized zeolite using the reaction between alkali(NaOH and KOH) and fly ash first. Aiming at the practical requirements on adjusting adsorption profile of Daqing Oilfield, the paper groped the technical method to partly transform the modified fly ash into zeolite under the hydrothermal condition. On the basis of summarizing and adsorbing the successful experience and shortcomings of fly ash and zeolite, the chemistry element and the outer structure characteristic of modified fly ash were also studied in the paper, and plugging effect of modified fly ash was evaluated. The results are pretty important for improving the plugging effect in the reservoir and the efficiency of water injection in oilfield.