The aim is to identify the structure of the hydrolyzate of betamethasone dipropionate, and to provide reference for the stability and formulation research.Forced degradation test of betamethasone dipropionate was carried out; the hydrolyzates were analyzed by HPLC, and the hydrolyzates were identified by MS; and the structures of the hydrolyzates were confirmed through comparison with synthetic impurities.The betamethasone dipropionate could be hydrolyzed under alk. and acid conditions, and produced different impurities.The two main hydrolysis products of betamethasone dipropionate were betamethasone 17-monopropionate, betamethasone 21-monopropionate, and could be further hydrolyzed into betamethasone.Betamethasone dipropionate could be easily hydrolyzed under alk. condition, and the degradation products could be further degraded.Under acid condition, the hydrolysis required relatively stronger reaction, and its degradation products could be degraded hardly.The hydrolysis impurities of betamethasone dipropionate under alk. and acid conditions were not the same.Three main hydrolysis products were betamethasone 17-monopropionate, betamethasone 21-monopropionate and betamethasone.