The invention relates to a preparation method of protein powder, in particular to a method for preparing protein powder by means of silkworm pupae. The method comprises the following steps of: degreasing; hydrolyzing: carrying out the enzymolysis on the silkworm pupae subjected to the degreasing step, wherein the enzyme dosage is 800-1000 activity units/ml, the enzymolysis temperature is 40-50 DEG C, the pH value is within 10-10.5, and the time for enzymolysis is 45-60min; grading: passing the degraded product through membrane separation plant, separating the separation solution with the molecular weight of 500-1000; concentrating: respectively concentrating the solution to be greater than 10% in percentage concentration; and deodorizing: respectively passing the concentration solution through a filtering device containing orange peel powder; and degreasing the silkworm pupa skins. The protein powder obtained by the invention is free from smell and has a certain aromas flavor, uniformmolecular weight distribution and high zinc content, and is particularly suitable for the preparation of various kinds of high-grade nutriments.