In order to further understand the impact of porous characteristics of the electrode materials on their electrosorption performance, we have conducted a systematic investigation on the cause effect relationship among various parameters, such as precursor concentrations, 3D rGO packing densities and out-of-plane porosities. Firstly, when the precursor concentrations for 3D rGO were changed from low to high concentrations, sample rGO-4 with medium GO concentration showed a dual pore size distribution with higher numbers of mesopores as well as the less stacking of the rGO sheets, demonstrated better electrosorption specific capacitance of 236 F g−1 than the low and high GO concentrations. Secondly, when the out-of-plane hierarchal pores were created by employing sacrificing nanocrystal-template crystals α-Fe2O3, sample T-rGO displayed higher micropore volume and the more active sites of the hierarchal pores, while its 3D graphene structure remained highly interconnected, both facilitated better ion access and achieved a specific capacitance of 409 F g−1. In capacitive deionization (CDI) experiments, sample T-rGO demonstrated a fast salt adsorption and desorption cycle and achieved 100% complete desorption/regeneration within an average of 59 min and a higher electrosorption capacity of 7.3 mg g−1. This study not only provided insights on the impact of rGO packing density on the electrosorption behavior, but also confirmed that creating additional out-of-plane nanopores by partial removal of template crystals post hydrothermal synthesis was a promising strategy to prepare porous electrode material for CDI.