Abstract: Today, most radar sites of the CINRAD have been established, and there is good condition to transmit radar base data to the regional center. To fully utilize the advantage of the Doppler weather radar network, and improve the capability of mesoscale disaster weather early warning, study about weather radar 3-D mosaic has been made in recent years, and the Doppler weather radar 3-D digital mosaic system is developed for the first time in China based on these research results. It introduces the design, system structure, main function modules, data process flow, and corresponding algorithms of the system, analysis software performance, practicality and reliability of the mosaic results, study methods to discriminate two important factors affect the mosaic results.The system includes the following modules: Base data loading, data time matching, data quality controlling, coordinates conversion of single site base data to Cartesian coordinates, reflectivity mosaic for all sites in the region, and the generation of series of derived products. It can provide quality controlled base data, 3-D reflectivity grid data of single site, 3-D mosaic reflectivity and some derived products base on mosaic base data, which are useful not only for operational work, but also for scientific research. It can run real time for the region with around fifteen radars, at intervals about 6 minutes, with the horizontal resolution of about 1 km, and at least 20 vertical height levels.Operational running on trial proves that the system is steady. Case study results show that the 3-D mosaic result with high time and spatial resolution is reliable, it provides advantage for analyzing mesoscale and small-scale severe weather, and supplies data basis for developing now-casting and some other works. Besides, the observation errors and position errors are two important cases which influence the mosaic results, and they can be determined easily by analyzing outputs of the system itself. The system is running on trial currently. It's planned to upgrade the system for business, after adding some functions and useful derived products in the near future.