The invention discloses a preparation method of collagen fibers. The preparation method comprises the following steps that extrusion molding is performed on a spinning solution on a dry-wet method spinning device, a spinning fine flow extruded from a spinning nozzle passes through an air layer with the length being 6-10 mm and then enters a coagulation bath for coagulation, and drying is performedto obtain nascent fibers, wherein a distance between the liquid level of the coagulation bath and the bottom of the coagulation bath is larger than 200 mm. The method provided by the invention can obtain the collagen fibers with the tensile strength being further improved.