This paper presents the development processes of a microwave radiometer for remote sensing of water surface temperature. Achieving the measurement accuracy within $2^{circ}C$ for water surface temperature of $5{sim}30^{circ}C$, the requirements and specifications of the microwave radiometer and its receiver are drawn. The receiver with high gain, high sensitivity is designed and implemented. The receiver has the bandwidth of 50 MHz, the system gain of 45.2 dB and the sensitivity of 0.56K at 5.02 GHz. The effectiveness of the developed microwave radiometer in the measurement of water surface temperature is demonstrated experimentally. The results show the microwave radiometer can detect water surface temperature for $7.5{sim}18^{circ}C$ within the accuracy of $0.45^{circ}C$.