step (1) two sets of modification devices are used to jointly treat fumed silica, each of which includes a reaction furnace and a gas separator; the fumed silica is treated with a modifier in the reaction furnace of each set of modification devices, and two groups of modified fumed silica and exhaust gas are obtained respectively;

step (2) the exhaust gas obtained in the step (1) is separated respectively to obtain unreacted modifier and by-products; and the obtained by-products are input into the reaction furnace of the other set of modification devices as reaction assistants to participate in the modification reaction; and the obtained unreacted modifiers are returned to the reaction furnace of the original modification devices for repeated use;

wherein, the modifiers used in the two sets of modification devices are different from each other and are selected from organochlorosilanes, alkylsiloxanes, alkylsilazanes, hydroxyl-terminated polysiloxanes and cyclosiloxanes; wherein, the modifiers used in the two sets of modification devices are not both selected from hydroxyl-terminated polysiloxanes or cyclosiloxanes.