The invention relates to a method for preparing hydrocortisone. The method includes: subjecting a cortisone acetate raw material to sites No. 3,20-keto protective reaction, site No.11-keto reduction reaction, site No.21-hydroxy esterification reaction, sites No. 3,20-ketone deprotection reaction, and site No. 21-acetate hydrolysis to obtain hydrocortisone. The method provides a new synthetic route containing esterification and deprotection in order, greatly improves the reaction selectivity, easily separates deprotection reaction products and avoids the posttreatment of tedious several times of extraction of a large amount of solvents in the traditional deprotection reaction process, and also avoids the side reaction caused by quenching reaction in the posttreatment of the traditional process; and the ester hydrolysis reaction is carried out under protection of inert gases in a mixed solvent, so as to avoid by-products produced in the hydrolysis reaction. The process route of the invention is novel, simple for operation, low in production cost, and applicable to industrial scale production.