The invention relates to a method for preparing natural fibers by means of cotton stalk bark. The method is characterized by comprising the steps of cotton stalk peeling, pre-processing, biological extraction, instant explosion, hot washing, softening and drying which are conducted sequentially. In the biological extraction process, water, enzyme complexes AE, DT and OK are added into the well processed cotton stalk bark obtained from the pre-processing process for reaction for 1-2 hours under the condition of 70-95 DEG C. The preparing technology solves the problem that cotton stalks are hard to peel, most impurities on the surface of the cotton stalk bark are removed by means of the combination of the enzyme complex biological extraction process and the instant explosion technology, cellulose purification is achieved, and the prepared cotton stalk bark natural fibers have excellent performance with dry strength>3.12cN/dtex, wet strength>1.79cN/dtex, wet modulus>0.48cN/dtex and dry strength variable coefficient<1.55%.