The removal performance of nitrate using capacitive deionization (CDI) of activated carbon (AC)-based electrodes were studied. The AC electrode was prepared and the effect of cell voltage, flow rate and initial solution concentration on ion removal were investigated. Furthermore, the AC was modified with phosphoric acid (ACP) and the surface structure of AC and ACP were analyzed. The results showed that the specific surface area of AC increased by 10.71% after the modification. The mesopore ratio and micropore ratio increased by 14.69% and 24.06%, respectively. The optimal conditions of AC electrode was a voltage of 1.4 V and flow rate of 20 mL/min while the ACP electrode was a voltage of 1.4 V and flow rate of 10 mL/min. The electrosorption capacity of ACP electrode was improved and the unit of electrosorption load was high to 19.28 mg/L. For the AC or ACP electrode, the nitrate removal efficiency decreases with the increase in the initial feed solutions, but the unit electrosorption load gradually increased with the improvement of initial feed solutions' concentration and the ACP electrode was superior to the AC electrode. Therefore, the ACP electrode would be suitable for the application of CDI on the nitrate removal.