The utility model discloses a multifunctional digestion device applicable to the total nitrogen determination pretreatment of a biological sample. The multifunctional digestion device comprises a digestion pipe (1) and a backflow pipe (2), wherein the digestion pipe (1) is in movable fit with the backflow pipe (2). The multifunctional digestion device is provided with a sealable backflow device with a filtration function, so that a certain pressure can be applied to a sample during digestion, a certain air condensation backflow and pressurizing effect is achieved, functions of sample digestion, volume determination and filtration can be completed, and the multifunctional digestion device is applicable to the digestion treatment of total nitrogen and protein samples of a plant. The multifunctional digestion device is simple in structure, easy to operate, stable and reliable in operation, and high in digestion efficiency; the operation steps of putting the digested sample into a volumetric flask and performing filtration are eliminated; the multifunctional digestion device is cooperatively used together with a digestion furnace with 40 to 50 digestion holes on the market; the digestion capacity of the sample is greatly improved.