The invention relates to a medicinal material scattering preventing device in the traditional Chinese medicinal material microwave drying process. The medicinal material scattering preventing device comprises a rack, a metal box, a conveying belt and roller sets. The metal box is arranged in the middle portion of the rack. The conveying belt is arranged on the rack and penetrates the metal box. The multiple roller sets are arranged in the operation direction of the conveying belt. The medicinal material scattering preventing device further comprises a microwave generator and anti-deflection set racks. The microwave generator is arranged in the metal box. The anti-deflection set racks are arranged on the two sides of the conveying belt. A lug plate frame of the anti-deflection set rack on each side is provided with two anti-deflection wheels, wherein the two anti-deflection wheels are arranged above and below the conveying belt and used for clamping the conveying belt. The lug plate frame on each side is further provided with anti-clamping wheels, wherein the anti-clamping wheels are arranged between the corresponding two anti-deflection wheels, and the axis of each anti-clamping wheel is perpendicular to the axis of the corresponding anti-deflection wheel. An anti-deflection device of a belt conveyor is suitable for being used in a microwave dryer and has the advantages of being stable in running, low in fault rate and long in service life.