The conversion of α-HMX to β-HMX was studied by the hydrothermal method, that is, when the solvent is deionized water, α-HMX can be converted to β-HMX. It was confirmed to be β-HMX after being characterized by mid-infrared spectroscopy, and its crystal form was further observed by high-power optical microscope, which was consistent with the infrared characterization results. The method is simple to operate, green and safe, reduces the production cost, and also solves the problem of traditional transcrystallization waste liquid treatment. [ABSTRACT FROM AUTHOR]