The invention provides a method which is used for extracting and preparing a black carbon adsorption material by taking plant ash as the raw material. The method comprises the following steps: firstly, a hydrochloric acid solution, the concentration of which is 0.5-2.0 mol/L, is used for processing the plant ash for 3-8 times, each time lasts for 2-6 hours, deionized water is used for fully washing after solid masses are obtained, and then the next step is carried out; secondly, the solid masses obtained in the step one are processed by a mixed acid solution containing 0.25-1.0 mol/L of hydrochloric acid and 0.25-1.0 mol/L of hydrofluoric acid for 3-8 times, each time lasts for 2-6 hours, and the deionized water is used for washing the obtained solid masses until the pH of a flushing fluid is neutral; thirdly, the solid masses obtained in the step two are dried, ground and screened, so as to obtain the more uniform black carbon adsorption material. The method of the invention provides a way for treating a great deal of surplus plant ash in rural districts; at the same time, the black carbon adsorption material obtained by the method of the invention has the advantages of fine particles, high carbon content, large specific surface area and low cost, and can be widely applicable to the adsorption removal of pollutants in various polluted waters.