The invention provides a preparation method of a phenoxymethylpenicillin potassium tablet. The preparation method comprises the following steps of (A) mixing phenoxymethylpenicillin potassium, microcrystal fibers, pregelatinized starch, carboxymethyl starch sodium and an ethanol solution of povidone K30, and carrying out wet granulation to obtain wet granules; (B) drying the wet granules, carrying out size stabilization, then, mixing the wet granules, magnesium stearate, superfine silica powder and carboxymethyl starch sodium, tabletting and coating to obtain the phenoxymethylpenicillin potassium tablet. According to the preparation method, carboxymethyl starch sodium is divided into two parts, wherein one part is used for granulating phenoxymethylpenicillin potassium, and the other part is used for totally mixing and tabletting after granulating; and due to the adoption of the operation, the phenoxymethylpenicillin potassium tablet prepared by using the preparation method provided by the invention is good in stability within a storage period, and the problems that related substances are increased within the storage period of the phenoxymethylpenicillin potassium tablet and the disintegration time limit of an intermediate product is unqualified are solved.