The invention discloses a middle-low-radioactivity nuclear waste treatment device. A storage barrel of the device comprises a barrel body, a barrel cover, a passive exhaust valve and a dewatering and filtering assembly; the barrel body and the barrel cover are each integrally formed through crosslinked polyethylene, the barrel body is provided with an opening, and the barrel cover is connected to the opening of the barrel body in an openable and sealed mode and provided with multiple exhaust vents; the dewatering and filtering assembly is arranged at the bottom of the barrel body and can be connected with an external pneumatic diaphragm pump, and the passive exhaust valve is arranged on the barrel cover. Air in the barrel body is exhausted through the passive exhaust valve and the exhaust vents, therefore, nuclear waste can keep the certain pressure during treatment, and the phenomenon that the storage barrel is expanded to be broken due to the fact that the contained materials are decomposed cannot occur; the barrel body and the barrel cover which are integrally formed through crosslinked polyethylene are stable in chemical property and high in corrosion resistance, the nuclear waste can be directly contained in the storage barrel to be stored safely for a long term, the swelling and fracturing phenomena cannot occur, and radioactive liquid cannot be leaked to cause environmental pollution; in addition, the capacity rate of the nuclear waste is greatly increased, and the treatment device is simple in structure.