The invention relates to a method for preparing a nanometer microcapsule and aims at providing a method for preparing an inorganic nanometer microcapsule by one step. The method includes that an emulsification agent and a PH regulator are dissolved into water; a monomer, a small molecular hydrocarbon template compound and a co-stabilizer are mixed and added into the mixed solution obtained above,and then ultrasonic dispersion is carried out to obtain a stable miniemulsion; the temperature of the obtained miniemulsion is adjusted to 30 to 80 DEG C; the inorganic nanometer microcapsule with aninorganic compound as a shell layer and the small molecular hydrocarbon as a core is obtained after reaction for 3 hours to 5 days. The method has simple preparing process and can stably obtain the inorganic nanometer microcapsule which has high thermal, chemical and mechanical stabilities; simultaneously the porous structure of the shell layer is more beneficial to the substance exchange betweenthe covered object and the outside environment; besides, the size of the microcapsule and the thickness of the shell layer can be conveniently realized by adjusting the proportion of the monomer and the small molecular hydrocarbon, the water-oil ratio and the categories and concentration of the emulsification agent when the invention is used for preparing the microcapsule.