The invention provides a preparation method of a new adsorbent, the method uses a dendritic polymer to modify a graphene oxide adsorption material, and the graphene oxide adsorption material modified by the dendritic polymer can effectively adsorb lead ions, cadmium ions, manganese ions, copper ions and other heavy metal ions in wastewater. The method is as follows: first using graphite powder as a raw material to prepare multilayer graphene oxide by concentrated sulfuric acid, potassium permanganate and hydrogen peroxide oxidation, fully dissolving the graphene oxide in ethanol with the aid of ultrasonic, then adding a certain amount of the dendritic polymer for water bath reaction at 30-80 DEG C for 6 to 48 hours, performing vacuum suction filtration of an obtained product, then washing with the ethanol, and then drying at 50-100 DEG C to obtain a heavy metal adsorption material. SEM (scanning electron microscope) pictures show that the adsorbent has a loose structure, and the adsorbent has a good application prospect in heavy metal adsorption field. Adsorption experiments show that, under the condition of normal temperature, the adsorbent has a good adsorption capacity to the lead ions, cadmium ions, manganese ions and copper ions, and especially has a strong adsorption capacity to the lead ions, and the maximum adsorption amount can reach 300mg/g above.