A pulp mixing device, comprising a mounting frame (1), a pulp mixing tank (2), a pulp adding tank (3), a cooling mechanism and a pulp discharging mechanism; the pulp adding tank (3) is movably provided below the pulp mixing tank (2), the cooling mechanism and the pulp discharging mechanism, and a mass scale (4) is provided below the pulp adding tank (3); a stirring cavity is formed in the pulp mixing tank (2), and a stirring paddle is provided in the stirring cavity; a stirring motor (5) is disposed on the pulp mixing tank (2); a discharge port (24) is formed at a bottom portion of the stirring cavity; an oil bath cavity (21) is formed between the pulp mixing tank (2) and the stirring cavity; the cooling mechanism comprises a lifting cylinder (82) and a lifting seat (8); the lifting seat (8) is provided thereon with a rotating paddle and a rotating motor (81); the lifting cylinder (82) is disposed on a mounting frame (1); an output end of the lifting cylinder (82) is connected to the lifting seat (8); the pulp discharging mechanism comprises a piston (91) and a driving cylinder (9); the piston (91) is connected to an output end of the driving cylinder (9), and the piston (91) is provided with an elastic sealing ring (92) along the circumferential direction; and a pulp outlet (32) is formed at a bottom portion of the pulp adding tank (3).