HY-2A satellite is China's first ocean dynamic environment satellite. The microwave radiometer is one of the four microwave payloads of the satellite, which is mainly used for measuring parameters including sea surface temperature, wind speed, water vapor and liquid water etc. The microwave radiometer is a conical scanning radiometer, real time calibration with cold sky and warm load on board, cover frequency from 6 GHz to 37 GHz. This paper introduced the design of instrument including system design, antenna design, receiver design and balance design etc.