The invention aims to provide a method for synthesizing a Y-shaped molecular sieve by taking tailings produced by acid-process aluminium extraction of coal ash as a raw material. The method comprises the following steps: (1) preparation of a structural guiding agent, (2) dissolution, (3) preparation of reaction gelatin, (4) crystallization and (5) post-processing. The Y-shaped molecular sieve product prepared according to the method provided by the invention has a favorable crystallization property. The method provided by the invention is simple and feasible, and can be widely applied in the field of chemical engineering, and is easy for reaction process control.