The invention discloses a preparation method of fine diatomite. According to the invention, method replacement and step dispersion are carried out on the most time-consuming delamination and purification procedures in the production process, the purification procedure adopts a mixed method, a scrubbing procedure is refined, and by means of coarse crushing, fine crushing and grading, original soil can be finely crushed into tiny particles, and at the same time a lot of impurities are removed in advance, thus greatly saving the consumption of water and time at the earlier stage of scrubbing, then dispersion and chemical acid leaching are carried out, in the layering procedure, a centrifuge is employed for centrifugal separation, and a lot of impurities are removed in advance in the earlier grading process, so that the efficiency of the layering procedure is also improved effectively. According to the method, the procedures are broken down, and an optimal production method is adopted directed at the characteristics of each step, although the upfront investment is increased to certain extent, the later production efficiency is obviously improved, and the fineness of fine diatomite is guaranteed.