To get an effective electric desalination system, the electrosorption performance of a capactive deionization(CDI) and a membrane capactive deionization(MCDI) was compared. The electrosorption capacity and electrosorption rate of CDI and MCDI with different salt concentrations were studied when powdered activated carbon was used as the electrode material. The results showed that as the salt concentration increased from 0.05 to 0.5 g／L, the electrosorption capacity of MCDI increased dramatically from 99.4 to 694.4 mol／g, while the electrosorption capacity of CDI just increased from 80.3 to 135.7 μmol／g.