The invention discloses a wet spinning method for preparing cellulose acetate fiber. The wet spinning method comprises the following steps: grinding solid cellulose diacetate, of which the degree of acetylation is 2.1 to 2.8 and the water content is 1 to 7 percent, into powder; adding the cellulose diacetate powder and an organic solvent into a dissolving tank, and carrying out sufficient stirring for mixing, and raising the temperature for dissolution, wherein the mass ratio of the cellulose diacetate powder to the organic solvent ranges from 1:3 to 1:7, the dissolving time is 0.5 to 8 hours, and the dissolving temperature is 35 to 120 DEG C; filtering and deforming a dope obtained after dissolution to obtain a spinning dope; after the spinning dope passes through a metering pump and a filter, spraying the filtered spinning dope from spinneret orifices to enter a coagulation bath to obtain nascent fiber, wherein the concentration of the coagulation bath is 25 to 70%, and the temperature is 20 to 90 DEG C; preparing a finished acetate fiber product from the nascent fiber through drafting, washing, oiling and drying. The cellulose acetate fiber prepared according to the method disclosed by the invention has excellent indexes, good mechanical properties, and remarkably improved dry strength and wet strength; the preparation process is simple, feasible, and easy to control; the solvent cost is low.