The invention discloses a full bio-based emulsifier as well as a preparation method and an application thereof, and belongs to the field of polymer materials. The full bio-based emulsifier is preparedfrom epoxy vegetable oil, which is one of renewable resources, by ring-opening reaction with natural dibasic acid, and the emulsifier is applied to preparation of anionic waterborne polyurethane emulsion. The epoxy vegetable oil and the natural dibasic acid are applied as emulsifier raw materials, a positive reference value is provided for broadening the application and increasing added value ofnatural oil products, and a positive role is also played in reducing environmental issues caused by consumption of petroleum non-renewable resources or replacing the petroleum non-renewable resources.Compared with DMPA (dimethylol propionic acid) and DMBA (dimethylbenzanthracene) which are solid at normal temperature, the prepared full bio-based emulsifier has larger contact area with other raw materials during reaction, and is mixed more uniformly and higher in reaction speed; the emulsifier is prepared from vegetable oil and has better water resistance and thermal stability due to triglyceride structure.