In this work, the hierarchically porous biomass carbon (HPBC) was originally prepared for desalination through a simple activation of cheap biomass carbon (BC). Such crucial activated conditions as the KOH/C ratio, the activation time and the activation temperature were deeply investigated. It is demonstrated that the activated conditions had a great influence on the structure properties and electrochemical performance. According to structure and surface analyses, the HPBC with larger surface area and hierarchical porous structure could be well obtained in suitable activation conditions. The electrochemical analyses showed that the HPBC showed increased electrosorption capacitance, lower inner resistance and good stability, which can be attributed to large accessible surface area and smooth ion transportation. In the further desalination test, the HPBC electrode exhibited enhanced desalination efficiency and capacity. Hence, HPBC can be a promising candidate electrode material for desalination with low cost and high efficiency.