Abstract: The application of activated brackish water in the water treatment and agriculture fields has been getting a lot of attention. The activated brackish water usually has different impact on the growth of plant, and a reasonable index is necessary for evaluating the effects of different activated brackish water. In this paper, a laboratory experiment was carried out to investigate the physical and chemical characteristics of the NaCl brackish water, which were set as different salinity (0.1, 1, 2, 3 and 5 g/L). The magnetized and ionized methods were adopted to activate the brackish water, and the technical requirements of the ionized activation system of brackish water were ascertained. Meanwhile, the changes of surface tension coefficient, dissolved oxygen, electrical conductivity and pH value of activated brackish water were studied by the laboratory test. The results indicated that there were stable grounding current and activation effects, when the grounding resistance was less than 5 Ω. Furthermore, the changes of the physical and chemical characteristics of the activated brackish water were extremely remarkable. The surface tension coefficient reduced significantly, while the change of dissolved oxygen was opposite. In the meantime, the electrical conductivity and pH value were affected at different degrees. With the increase of brackish water salinity, the surface tension coefficient increased accordingly, while the dissolved oxygen changed oppositely. The surface tension of the activated brackish water relatively reduced by 9.14%-13.84% in the brackish water with the salinity of 5 g/L, while the dissolved oxygen relatively increased by 8.04%-10.23%. According to the surface tension′s relative reduction, the difference was obvious among different activated treatments. The ionized activation treatment was superior to the magnetized water, and the stainless steel ionized separator (SIW) was better than the one with magnesium core(MIW). There was the optimum magnetization for permanent magnet, and the surface tension′s relative reduction had the maximum value under the magnetic field strength of 3 000 Gs. The variable frequency (VF) magnetized brackish water treatment was stable, but still less than the optimum magnetization. On the basis of the value of dissolved oxygen relative increment, the distinction was also significant among different activated treatments. The value of oxygen relative increment had the maximum value under the magnetic field strength of 3 000 Gs. When the salinity exceeded 3.0 g/L, the effect was greatly reduced. Foremost, there existed a significant index function relationship between the relative reduction of surface tension and the relative increment of dissolved oxygen(R²>0.88, P<0.05). The relationship could be used to estimate the corresponding relative increment of dissolved oxygen, when the relative reduction of surface tension was known. In conclusion, the surface tension′s relative reduction can be used to quantitatively evaluate the changes of the physical and chemical characteristics of the activated brackish water. This study may provide valuable information for the application of activated brackish water in agriculture irrigation.