Based on the statistical analysis of the data from blind water sample assessment in past 5 years conducted by the China Meteorological Administration that Anhui Provincial meteorological acid rain observatories participated in, the main reason for the conductivity decline of blind water samples in acid rain observation stations of Anhui Province in 2014 is the change of instrument electrodes. It is concluded that the Model990 AcidRain Gauge presents obviously larger systematic error in measuring the K with the platinum black electrode. However, the physical shape of the lighttype conductive electrodes remains the same, and its cell constant is almost invariant. Thus, they can be used for a long term via demarcating with standard solution. In order to improve the accuracy of conductivity Kvalue measurement, it is suggested that stations should use the standard solution with a conductivity of 84.3 or 146.5 μS〖DK〗·cm-1 which is commercially available to demarcate the device electrodes regularly every year. In addition, recommendations are proposed for the security and verification system of acid rain detection equipment.