Recently, some deformation measured by non-stress meters are found abnormal, which affects the reliability of observation results of strain meters. In view of this, we propose the basis, criteria and methods to distinguish abnormal data by researching the regularity of autogenous volumetric deformation of concrete. We also suggest some methods to correct the abnormal data of non-stress meters, and applied them to the discrimination and modification of non-stress meter results for Ertan arch dam. The results prove that the modification methods are effective, and the corrected results reflect the actual stress of Ertan dam.