Abstract: The microwave radiometer is a microwave remote sensing device that uses passive reception of microwave signals from atmospheric radiation to convert the radiant temperature of an object, and a D-band terahertz radiometer is designed in the paper through the key technologies of antenna feeder network and terahertz receiver. The radiometer is composed of a Cassegrain antenna and a D-band direct detection receiver, and the whole machine is fully localised. In the frequency range, the noise figure of the radiometer is less than 4.5 dB, the linearity reaches 0.999 9, the sensitivity reaches 0.1 K (@integration time 20 ms), and the power consumption of the whole machine is less than 2.8 W. The D-band dual-polarisation radiometer is an important part of the microwave imaging detector, and it can be used for observing the parameters of the atmospheric window.