The present invention discloses a method for preparing an anti-heart-failure medicine LCZ696. The preparing method comprises the following step (formula (I)): in an organic solvent, a Sacubitril dicyclohexylamine salt reacts with valsartan under the effect of a sodium hydroxide aqueous solution, and the anti-heart-failure medicine LCZ696 is obtained. The preparing method of the present invention is simple in process and omits the procedures of ion exchange from a sodium salt to a calcium salt and hydrochloric acid dissociation in an existing production process, residues of calcium ions are avoided, and the production efficiency is effectively improved.