Electrodialysis (ED) technology has been paid special attention in reclamation of high salinity effluents. Therein, the attempts on how to separate out scale-forming cations are never ending. Different from a conventional scheme, an on-line endowment of mono-cation permselectivity to a conventional ED stack was put forward in this work by electro-deposition of branched polyethyleneimine with an optimized molecular weight. Subsequently, series of work performances, including limiting current, mono-cation permselectivity, permselectivity between specific anions, water transport behavior, current efficiency and energy consumption, were investigated in reclamation of a typical saline wastewater. The pilot-scale ED experiments showed that the modified ED stack displayed a significant mono-cation permselectivity, for examples, P-Na+(Ca2+) and P-Na+(Mg2+) were reduced from 0.36 and 0.81 to 0.11 and 0.12, respectively. Interestingly, a certain permeability priority for SO42- was also achieved at the same time. Moreover, the five-month service life tests indicated the ED stack can maintain a stable separation performance. On the other hand, some problems induced by the modification were also revealed, such as the facilitated water transport and the increase of energy consumption. Anyway, it is reasonable to believe that the scheme should have broad and promising application perspectives due to its effectiveness, economy and simplicity.