The invention belongs to the technical field of inorganic non-metallic ferrite material preparation, and relates to a method for preparing a ferrite nano crystal assembly body by means of a solvothermal method. The same set of production equipment is adopted for regulation and control to prepare ferrite nano crystal assembly bodies of two different structures, namely the normal spinel structure and the inverse spinel structure, and the problem that multi-component inorganic non-metal ferrite nanocrystal assembly bodies are single in structure and effective regulation and control can not be conducted is solved. Ferric chloride hexahydrate, nickel chloride and manganese acetate serve as precursors, anhydrous sodium acetate serves as a surfactant and a stabilizer, ethylene glycol serves as a solvent, the nano crystal assembly body is prepared, polyethylene glycol serves as an interface regulating agent, the preparation technology is simple, the principle is reliable, the investment and operation cost is low, the product quality is stable, the batch preparation of two kinks of different products by means of the same set of production equipment in the industrial production process is achieved, fixed-asset investments are saved, the economic benefits are increased, and the method has a good economic value and a broad market application prospect in the magnetic material preparation industry.