The invention relates to a preparation method of a polyaniline/Ag nanometer composite material, in particular to the method of adopting hydrogen peroxide as the oxidant to induce aniline to polymerize and as the reducing agent to reduce silver nitrate, and utilizing the sonochemical method to prepare polyaniline/Ag nanometer composite material. Nitric acid is added into aniline to make the nitricacid solution of aniline; while magnetic stirring, the nitric acid solution of aniline is dripped into the silver nitrate solution; while further magnetic stirring, the prepared hydrogen peroxide solution is dripped into the mixture; and then the mixture is put in an ultrasonic reactor after dripping is finished for ultrasonication, standing, and then conducting centrifugal separation, solid washing and drying to get green powder. The invention designs to use the double situ-compound method of adopting hydrogen peroxide as the oxidant to induce aniline to polymerize and as the reducing agent to reduce silver nitrate; as the reaction is very slow under magnetic stirring, therefore, the energy produced by ultrasonication is used for speeding up the reaction. The method has simple productionprocess, convenient operation and less equipment investment, and better solves the agglomeration problem of silver nanometer particles; the silver nanometer particles in the obtained composite material can evenly distribute in the polyaniline matrix.