The invention discloses a back device for carrying a mortar base plate. Each one of four corners of a back cushion is provided with a fixing belt and a four-beam structure and the fixing belts and the four-beam structures are matched mutually. A base plate back support comprises an inverted U-shaped back support frame, a tray and spacing rings. The tray is arranged at the bottom of the inverted U-shaped back support frame. The spacing rings are arranged at two opposite sides of the inverted U-shaped back support frame. The back cushion passes through the fixing belts and the four-beam structures of the inverted U-shaped back support frame and is connected to the base plate back support. A shoulder cushion symmetrically comprises a left fixing belt and a ring fixing belt. Upper ends of the left fixing belt and the ring fixing belt are assembled to handles at the base plate upper-part. Lower ends of the left fixing belt and the ring fixing belt are assembled to a square ring at the base plate lower-part. A waistband is provided with a left waist fixing belt and a right waist fixing belt assembled to the square ring at the base plate lower-part. The gravity centre position of the back device for carrying the mortar base plate can be adjusted according to height and weight of people so that in carrying, the gravity centre position is appropriate, and comfortable, safe, convenient and fast carrying is realized without both hands.