The invention discloses a duct propulsion system based on a multi-rotor unmanned aerial vehicle, and belongs to the technical field of an unmanned aerial vehicle. The system comprises a multi-rotor unmanned aerial vehicle, a first cloud deck interface, a duct buoyancy module and a second cloud deck interface, wherein the multi-rotor unmanned aerial vehicle and the first cloud deck interface are rigidly connected; the lower part of the first cloud deck interface is rigidly connected with the duct buoyancy module; the upper part of the second cloud deck interface is rigidly connected with the duct buoyancy module; a reserved interface is arranged at the lower part of the second cloud deck interface, and can be connected with the carried cloud deck or other equipment. Through the use of the general cloud deck interfaces, the rigid mechanical combination can be realized with various models of consumption stage multi-rotor unmanned aerial vehicles; in addition, different ducts or batteries can be carried according to different load bearing requirements so as to improve the maximum buoyancy; the additional arrangement of the complicated duct control system is not needed; the great modification potentials and design margin are realized; through being compared with a redesigned unmanned aerial vehicle, the duct propulsion system saves great cost.