The invention relates to the field of injection molding machines, in particular to a heating device for the injection molding of an injection molding machine. The heating device comprises a material feeding mechanism and a heating mechanism, wherein the material feeding mechanism comprises a material collecting hopper, a material discharge pipe and an outer protective casing; the heating mechanismcomprises a first heating mechanism, and a heater is arranged at the side part of a circulating pipe; a spiral rod is rotationally connected in the circulating pipe, and a second piston is fixedly into the spiral rod in a penetrating way; a first piston is fixedly arranged at the top part of the spiral rod, and is glidingly connected to the interior of a sealing box; the sealing box is communicated with the circulating pipe; a hydraulic machine connecting pipe and a water intake pipe are arranged at the side part of the sealing box; the bottom part of the circulating pipe is communicated witha slow flowing pipeline; the bottom part of the slow flowing pipeline is communicated with a second heating mechanism. The heating device has the advantages that the flowing route of the raw materialin the limited space is increased, and the land occupation area is reduced; the raw material is in full contact with the heater, so that the heating efficiency is improved, and the cleaning is convenient and rapid.