The invention provides a method for improving the quality of a fly ash concrete admixture. 50 to 97 percent of undisturbed fly ash, 1 to 30 percent of blast furnace slag, 1 to 30 percent of tailings of magnet quartzite type iron ore or quartzite tailings or marble tailings or granite tailings or stone powder scrapped during stone processing, 0.1 to 1 percent of melamine formaldehyde resin sodium sulfonate, in weight percentage, are mixed and ground together until the triage of a 0.045mm square-mesh sieve is less than or equal to 12 percent. The off-standard fly ash and III-grade fly ash with a gross amount over 80 percent can be improved into the I-grade fly ash or II-grade fly ash according to the method, the utilization value of inferior fly ash can be raised substantially, and the method has advantages of good economic benefit, enlarging the amount of admixture, saving cement and improving the performance of concrete.