The results of interstation comparison of 7 pH measurements and two conductanc e measurements of blind samples from the Acid Rain Monitoring Network of China M eteorologicalAdministration (ARMN/CMA) since 1992 are presented. The diluted and pH modulat ed buffer solution was used as blind samples to prevent the changes during the t ransportation. The standard deviations of reported pH values were below 0.2 pH u nits, and its correlation with pH value of the sample was not significant. Stati stics showed the significant improvements of the error level of pH measurement o f blind samples corresponding to the system upgrading/quality control activities , such as the instrument renewal, personal training, and the enforcement of new technical regulation. Statistics also showed that bias of pH measurement of smal l part of stations with poor technical condition was featured with a relatively large negative value. To evaluate overall precision for both pH and cond uctance measurements of ARMN /CMA, Modified Median Absolute Difference (M.MAD) were cal culated according to the WMO recommended method. The M.MAD of pH measurement was in a range of 0.03～0.10 pH units, and that of conductance in 4%～5%.