A preparation method of sustained-release microparticles, characterized by comprising the following steps: 1) preparing a solid dispersion of a water-soluble drug and a biodegradable and biocompatible poorly water-soluble polymer, wherein the preparation comprises the following steps: i) completely dissolving the biodegradable and biocompatible poorly water-soluble polymer and the water-soluble drug in an organic solvent A to form a mixed solution of the drug and the polymer; and ii) adding the mixed solution into an organic solvent B or adding the organic solution B into the mixed solution to produce a uniform and fine precipitate, collecting the precipitate, washing the precipitate with the organic solvent B several times, and removing the organic solvent B to obtain a solid dispersion of the water-soluble drug and the poorly water-soluble polymer, wherein the organic solvent B is incapable of dissolving the poorly water-soluble polymer and the water-soluble drug, and wherein the organic solvent A is selected from at least one of glacial acetic acid, acetonitrile, trifluoroacetic acid and dimethyl sulfoxide; and the organic solvent B is selected from at least one of anhydrous diethyl ether, hexane and n-heptane; 2) dissolving the solid dispersion prepared in step 1) in an organic solvent C to form a solid dispersion emulsion, the organic solvent C being an organic solvent which is not capable of dissolving the water-soluble drug but capable of dissolving the poorly water-soluble polymer, has a boiling point lower than that of water and is insoluble or poorly soluble in water; 3) adding the solid dispersion emulsion obtained in step 2) into a surfactant-containing aqueous solution to form a uniform emulsion; and 4) solidifying microparticles in the emulsion by solvent volatilization or solvent extraction, collecting the microparticles, washing with ultrapure water several times to remove the surfactant attached to the surface of the microparticles, and drying to obtain the sustained-release microparticles; the water-soluble drug is at least one of a protein drug, a peptide drug and a nucleic acid drug. 1) preparing a solid dispersion of a water-soluble drug and a biodegradable and biocompatible poorly water-soluble polymer, wherein the preparation comprises the following steps: i) completely dissolving the biodegradable and biocompatible poorly water-soluble polymer and the water-soluble drug in an organic solvent A to form a mixed solution of the drug and the polymer; and ii) adding the mixed solution into an organic solvent B or adding the organic solution B into the mixed solution to produce a uniform and fine precipitate, collecting the precipitate, washing the precipitate with the organic solvent B several times, and removing the organic solvent B to obtain a solid dispersion of the water-soluble drug and the poorly water-soluble polymer, wherein the organic solvent B is incapable of dissolving the poorly water-soluble polymer and the water-soluble drug, and wherein the organic solvent A is selected from at least one of glacial acetic acid, acetonitrile, trifluoroacetic acid and dimethyl sulfoxide; and the organic solvent B is selected from at least one of anhydrous diethyl ether, hexane and n-heptane; i) completely dissolving the biodegradable and biocompatible poorly water-soluble polymer and the water-soluble drug in an organic solvent A to form a mixed solution of the drug and the polymer; and ii) adding the mixed solution into an organic solvent B or adding the organic solution B into the mixed solution to produce a uniform and fine precipitate, collecting the precipitate, washing the precipitate with the organic solvent B several times, and removing the organic solvent B to obtain a solid dispersion of the water-soluble drug and the poorly water-soluble polymer, wherein the organic solvent B is incapable of dissolving the poorly water-soluble polymer and the water-soluble drug, and wherein the organic solvent A is selected from at least one of glacial acetic acid, acetonitrile, trifluoroacetic acid and dimethyl sulfoxide; and the organic solvent B is selected from at least one of anhydrous diethyl ether, hexane and n-heptane; 2) dissolving the solid dispersion prepared in step 1) in an organic solvent C to form a solid dispersion emulsion, the organic solvent C being an organic solvent which is not capable of dissolving the water-soluble drug but capable of dissolving the poorly water-soluble polymer, has a boiling point lower than that of water and is insoluble or poorly soluble in water; 3) adding the solid dispersion emulsion obtained in step 2) into a surfactant-containing aqueous solution to form a uniform emulsion; and 4) solidifying microparticles in the emulsion by solvent volatilization or solvent extraction, collecting the microparticles, washing with ultrapure water several times to remove the surfactant attached to the surface of the microparticles, and drying to obtain the sustained-release microparticles; the water-soluble drug is at least one of a protein drug, a peptide drug and a nucleic acid drug.