The invention relates to a method for preparing and dissolving silk fibroin powder, which comprises the steps of degumming, pre-alkali washing, high-temperature high-pressure treatment, purification, pre-concentration, drying, and ultrafine grinding. The method of the invention adopts a high-temperature high-pressure method combined with ultralow-concentration alkali liquor to dissolve fibroin fibers, can completely dissolve fibroin fibers, and breaks the precedent that a high-temperature high-pressure method cannot dissolve silk fibroin; when compared with other technology in the prior art, the method adopts alkali liquor with an ultralow concentration, does not destroy the internal structure of natural silk fibroin, is simple and high-efficient in process, has significantly decreased cost, is short in production period, high in biological safety, simple and convenient, does not generate other wastes, and causes no environment pollution.