The invention relates to the technical field of compound synthesis methods, and discloses a method for synthesizing methoxyamine hydrochloride. The method comprises the following steps: adding water, sodium hydroxide, diacetylmonoxime and a phase transfer catalyst into a reaction kettle; after cooling, adding a methylation reagent; conducting standing for layering to obtain an organic layer, a water layer and a distilled water layer, collecting distillate, combining an oil layer and the distillate, and adding hydrochloric acid for mixing to obtain a mixed solution; feeding and rectifying the mixed solution from the middle of a rectifying column, recovering butanone and methanol at the top of the column, recovering a methoxyamine hydrochloride solution at the bottom of the column, and carrying out evaporating and dehydrating to obtain a concentrated solution; and cleaning a reaction kettle, wherein a stirring mechanism and a cleaning mechanism are arranged in the reaction kettle, the cleaning mechanism comprises a scraping plate, a spraying pipe, a lifting assembly and a rotating assembly, a water inlet pipe and a cleaning nozzle are connected to the spraying pipe, the reaction kettle comprises a kettle body and a kettle cover, the water outlet end of the cleaning nozzle faces the side wall of the kettle body, and the scraping plate is attached to the side wall of the kettle body. The method has the effect of conveniently cleaning residues on the side wall of the kettle body.