The invention relates to an automatic blending device for a tubular propellant and belongs to the field of propellant processing. The automatic blending device for the tubular propellant provided by the invention comprises feeding devices, transverse conveyor belts, a longitudinal conveyor belt and a collecting conveyor belt, wherein propellant grains processed in each batch are added into each of the feeding devices, each of the feeding devices propels the single propellant grain to each of the transverse conveyor belts, and the transverse conveyor belts convey all the propellant grains to the collecting conveyor belt through the longitudinal conveyor belt, so as to finish a blending operation. The automatic blending device provided by the invention realizes automatic operation of the blending process of the tubular propellant, so that the labor intensity of the worker is greatly reduced, and the work efficiency is improved; the blending quality is effectively controlled, and the consistency of the performance of the whole batch of products is guaranteed; meanwhile, manual operation is avoided, and safety accidents are avoided.