The invention discloses a low-temperature carbonizing device for producing carbon fibers, and belongs to the field of technologies for producing carbon fibers. The low-temperature carbonizing device comprises a furnace, a sealing device, an exhaust system, a protection gas supply device, a cooling chamber and a temperature detection control device. The sealing device is connected to two ends of the furnace, and the exhaust system is communicated with a hearth of the furnace. The cooling chamber is connected with a strand outlet of the furnace by a non-contact sealing device, and the temperature detection control device is connected with a temperature sensor of the furnace by a temperature detection circuit. The low-temperature carbonizing device has the advantages that the cooling chamber is arranged at an outlet end of the furnace, accordingly, the temperatures of strands drafted out of the furnace can be effectively reduced, the carbonized high-temperature strands can be prevented from being oxidized by oxygen in air, and the quality of the carbon fibers can be improved; the temperature sensor is mounted inside the furnace, and accordingly the internal temperature of the furnace can be monitored and controlled in real time.