The invention relates to an extraction method based on a waterhyacinth surface active agent substance. The extraction method comprises the following steps of: mashing waterhyacinth leaves, stems or stem leaves, adding an ethanol solution, leaching for 4-8 hours at 30-50 DEG C, filtering, repeating for 1-3 times to obtain a filtered solution, and carrying out concentration. The method is simple and convenient and is easy to implement, the operation is easy, the pollution is free, and a raw material is from a reproducible biomass resource. The natural active substance extracted by the method provided by the invention can notably reduce a surface tension effect, the natural active substance can serve as a foam suppressor and has the good foam repressing property and the defoaming property, and the natural active substance also can serve as a dispersant agent with superior performance after being compounded with a general surface active agent.