Abstract: In order to evaluate the accuracy of HY-2A (HaiYang-2A) CMR (Calibration Microwave Radiometer) offshore water vapor products, the data of GNSS (Global Navigation Satellite System) operational observation stations along the coast of China and the reanalysis data of ERA5 (European Centre for Medium-Range Weather Forecasts Reanalysis 5) are used as validation data. Firstly, the selected GNSS operational observation station data and CMR water vapor content data are spatial and temporal registered. The observation time of the two data is consistent, and the spatial distance is less than 100 km. Then, the PWV (Precipitable Water Vapor) over the GNSS operational observation station is retrieved by using the precise point positioning method, and the ERA5 PWV at the position of CMR water vapor content data is derived by interpolating the 1h resolution ERA5 reanalysis product. Finally, taking GNSS PWV and ERA5 PWV as references, the temporal and spatial distribution of accuracy and deviation of HY-2A CMR water vapor content products in 2015 is analyzed. The results show that the correlation coefficient r between CMR water vapor content and GNSS PWV and ERA5 PWV is higher than 0.96, and the average root mean square error is 3.17 mm and 1.58 mm respectively, which indicate a high accuracy of CMR water vapor content. There is no seasonal variability in the deviation of CMR water vapor content from GNSS and ERA5 PWVs, however, an increasing accuracy of CMR water vapor content with increasing latitude.