Abstract:To evaluate the method improvements on the blind sample preparation and the data calculation, this paper describes the method of the blind samples inter comparison study, which is conducted annually among the Acid Rain Monitoring Network of China Meteorological Administration (ARMN/CMA), and presents analysis on the pH and conductivity measurement deviations from 376 stations since early 1990s. The analysis indicates that the blind samples prepared during 2007-2017 by the improved method, which is inconsistent with WMO GAW protocol, cover the coincident ranges of pH, conductivity and ionic composition with the actual precipitation. The improved data calculation method adopted since 2005, which derives the statistical true value and the standard deviation of the pH measurement and conductivity measurement of the blind samples, shows obviously an improvement in reflecting overall status and annual performance changes of ARMN/CMA stations in pH and conductivity measurement. The annual blind samples inter comparison study is playing a key role in the ARMN/CMA quality management system.