Abstract: The atmospheric reanalysis in the East Asian region is the fifth sub-project of the key mission of China Meteorological Administration—"Meteorological Data Quality Control and Multi-source Data Fusion and Reanalysis". In this paper, the progress of the development of atmospheric reanalysis in East Asia is documented from four aspects of data collection, assimilation system, numerical model, and veri fications. In terms of observational data, of conventional ground-based observations and sounding, aircraft, GPS, radar, wind pro file, satellite observations have been collected, as well as data from field experiments. One of the characteristics of the regional reanalysis is that lots of observational data such as some conventional ground-based and sounding observations, and radar datasets are used, which are not shared with the Global Communications System (GTS). As for the data assimilation system, the Grids Statistical Interpolation (GSI) assimilation system is introduced and localized, especially with the radial wind radar assimilation operator improved. For the Weather Research and Forecasting Model (WRF-ARW) model, experiments of real cases and long-term simulations have been completed with multiple physical parameterization options, and the model con figurations have been optimized based on the experimental results. Besides, the NCAR Model Evaluation Tools (MET) has been introduced to build the veri fication system. At present, the reanalysis system has been completed and optimized. The experimental results show that the reanalysis system has a potential performance of improving the regional reanalysis based on a global reanalysis data. Therefore, the reanalysis system can be used to generate regional reanalysis datasets over East Asia in the future.