A mesoscale convective system (MCS) embedded in a cold frontal cloud system over Beijing on July 16, 2018 was investigated using X-band dual-polarization radar observations from Fangshan Station and sounding data from the Beijing Observatory. This study focused on hydrometeor identification and microphysical characterization, yielding the following key findings. 1) The ice-phase hydromorphic species above the 0°C layer differed in different stages and regions of this MCS. From the stage of development to maturity to dissipation, the main hydromorphic species in the region with combined reflectance larger than 40 dBZ were graupel and snow, and the proportion of ice crystals was relatively low. In the region with combined reflectance between 20 and 40 dBZ, graupel, snow, and ice crystals were the main hydromorphic species. In these two regions, the proportion of graupel gradually decreased with time, while the proportion of snow and ice crystals gradually increased with time. In the region with combined reflectance smaller than 20 dBZ, the proportion of graupel was very low, and the main hydromorphic species were snow and ice crystals, with the proportion of snow gradually decreasing with time, and the proportion of ice crystals gradually increasing with time. 2) The area of the 20–40 dBZ echo region in this MCS played a dominant role in precipitation area. 3) At the beginning of convection, satellite brightness temperature observation had a better monitoring effect on precipitation. The application of X-band dual-polarization radar data to analyze the microphysical characteristics of MCS is beneficial to understand the microphysical processes occurring in the system, and can provide a useful reference for the revision of the microphysical parameterization scheme.