Abstract: In response to the demand for high-precision noise transmission in millimeter and submillimeter waves, a high-temperature noise source applied in THz frequency band using microwave radiator is introduced, which can provide an equivalent output noise temperature of about 500 K with an uncertainty of less than 2%. The radiator is made of pyramid-shaped high-temperature absorbing material, with good homogeneity for both E and H surfaces. The constant temperature bath heating method effectively improves the temperature uniformity of the radiator. An improved rectangular horn antenna is used to reduce the port reflection and thus reduce the effect of the antenna on the equivalent output noise temperature.