In order to reduce the loss of data due to rainfall attenuation and to provide the "best" data for users, the master and diversity data in the path diversity reception mode are optimally synthesised to reduce the impact of rainfall on the Ka-band data transmission link of the Fengyun-4 geostationary meteorological satellite. In this paper, the rainfall fading budget model provided by the International Telecommunication Union's Radiocommunication Sector (ITU-R) is used to fully calculate the rainfall fading situation, and a data merit synthesis system is designed to discriminate the data quality by the fill and error codes of the Advanced Orbiting Systems (AOS) frame data, and to select high-quality data frame by frame for synthesis and distribution to users. Because of the different attenuation effects of rainfall on different frequency bands, the system was tested in a simulated operational environment using Ka-band and X-band data. The test showed that the data merit synthesis system was able to effectively judge the quality of the input data and generate distribution data that met the service requirements, effectively reducing the impact of rainfall on the Ka-band data. The results show that the data merit synthesis system can fully play its role in the path subset, ensuring the high-quality reception of meteorological satellite data and the use of Ka frequency resources.