The invention provides a preparation method of pure-phase bismuth ferrite. The method comprises a step of preparing a precursor liquid. Fe(NO3)3.9H2O and Bi(NO3)3.5H2O are dissolved in a solvent to obtain the precursor liquid with the metal ion concentration being 0.2 mol/L. Ammonia water is mixed with a ammonium bicarbonate solution to obtain a precipitating agent. In magnetic stirring, the precursor liquid is uniformly added to a precipitating agent solution dropwise till the pH value of a titration final point is controlled in 9-10. After titration is completed, stirring is continuously carried out to obtain a precipitate. The precipitate is allowed to stand and age, filtration is carried out, and the obtained product is washed with deionized water and absolute ethyl alcohol and is dried to obtain precursor powder. The precursor powder is put in a muffle furnace, the temperature is raised for calcination, and the obtained product is cooled to obtain pure-phase bismuth ferrite powder. The preparation method and the equipment are simple, and the pure-phase bismuth ferrite can be prepared in a large amount at one time. The preparation method is free of organic solvent and is green and eco-friendly, and the pure-phase bismuth ferrite is complete in crystallization and uniform in powder size.