The invention discloses a cement mortar protecting device for helical distributors, which comprises a pressure plate, an outer sealing cover, a sealing cover, a speed-reducer fixing plate, a rubber plate, an oil seal, a floating ring, a sealing ring and a check ring, wherein the sealing cover is fixedly connected with the speed-reducer fixing plate through a plurality of fasteners; the rubber plate is arranged between the speed-reducer fixing plate and the sealing cover; the oil seal is arranged in a ring groove of the oil seal inside the sealing cover; the floating ring is arranged in a floating-ring groove between the outer side of the sealing cover and the inner side of the outer sealing cover; the pressure plate is inlaid on the outer side of the outer sealing cover and is fixedly connected with the outer sealing cover through a plurality of fasteners; the pressure plate is axially and fixedly connected with a main shaft of a helical distributor through a set screw; and the check ring and the sealing ring are arranged in the pressure plate and the outer sealing cover respectively. The device adopts double sealing and the back extrusion effect of regularly adding grease to effectively prevent cement mortar from permeating a speed reducer, thereby greatly reducing the maintenance amount of the speed reducer and improving work efficiency.