The invention discloses a method for preparing collagen peptide. The method for preparing collagen peptide comprises the following steps: (1) mixing fishskin with water in a mass ratio of 1:(2-6), extracting for 1-3 hours at 90-100 DEG C so as to obtain an extract, and adjusting the pH value to 5-10; (2) adding an enzyme and an enzyme keep-alive agent into the extract of 45-75 DEG C for hydrolysis for 1-5 hours; (3) performing enzyme deactivation for 5-15 minutes at 85-100 DEG C so as to obtain enzymatic hydrolysate; (4) deodorizing, decoloring and filtering the enzymatic hydrolysate by using activated carbon, so as to obtain a destaining solution; and (5) performing ultra-filtration and freeze-drying on the destaining solution. By adopting the method for preparing collagen peptide, a product is high in yield, good in antibacterial property and good in beautifying and skin moistening effect. Raw materials of the collagen peptide are free of harmful substance, so that the environment is not polluted; and moreover the raw materials of the collagen peptide are wide in resource, the preparation process is simple, and the product has effects of maintaining beauty and keeping young, promoting cell growth and preventing aging.