The invention discloses a high-temperature diffusion device which comprises a furnace body. One end of the furnace body is provided with a furnace mouth, the other end of the furnace body is provided with a closed structure, and a furnace cover is arranged at the furnace mouth; a quartz boat is arranged in the furnace body, and silicon wafers are uniformly placed on the quartz boat; the upper end of the furnace body is provided with a first process gas inlet, a second process gas inlet and a third process gas inlet, and the lower end of the furnace body is provided with a tail gas exhaust port; the high-temperature diffusion device further comprises a gas flow stabilizing device which is arranged at the furnace mouth or the furnace middle or the furnace tail. According to the high-temperature diffusion device, the structure is simple, the gas flowing stability in the furnace body can be improved, the silicon wafer diffusion uniformity is guaranteed, and then the uniformity of a silicon wafer square resistor is guaranteed.