The invention relates to a method for treating high-concentration ammonia-nitrogen wastewater with a molecular sieve prepared from flyash, and belongs to the field of molecular sieve preparation. According to the method, the flyash wide in source and low in price is used as the synthesis raw material of the molecular sieve and has broad prospects, production cost is reduced, the waste material is used, which is of great significance in environment protection, and due to the large specific surface area of the flyash, the prepared molecular sieve has excellent treatment effect on the high-concentration ammonia-nitrogen wastewater.