The present disclosure relates to a preparation method of a trisodium AHU-377 and Valsartan co-crystal hydrate Form II. The preparation method comprises: firstly, preparing a clear solution of trisodium AHU-377 and Valsartan, the solvent of the clear solution comprises an anti-solvent and a good solvent of the target product Form II, and the boiling point of the good solvent is lower than that of the anti-solvent； secondly, evaporating the solution under vacuum to remove the good solvent and water from the system； and finally, optionally adding seed crystals of Form II or not and replenishing a mixture of water and a carrier solvent for stirring for crystallization. The method of the present disclosure can prepare Form II successfully, and the process is consistent and controllable. The obtained Form II product has high chemical purity, crystalline purity and good flowability； and the process can be scaled up, and meets the requirements of large-scale production.
