The invention discloses a quantitative liquid feeding device for a reaction still and an application method of the quantitative liquid feeding device. The device comprises a shell, the top of the shell is connected with a liquid injection pipeline, a quantitative liquid feeding assembly and a lifting assembly are arranged on the shell, the quantitative liquid feeding assembly comprises a flexible liquid storage container and a liquid collecting container, and the quantitative liquid feeding assembly is matched with the lifting assembly and connected with a stirring structure. According to the quantitative liquid feeding device, liquid ingredients large in proportion are added into the reaction still in batches and then fused and stirred with other ingredients, an equal quantity of small part liquid ingredients is added while stirring is carried out, and therefore stirring efficiency is improved; it is guaranteed that stirring and fusing are even, the product percent of pass is increased, and meanwhile the effect of avoiding waste is achieved.