Unravelling the adsorption mechanism is crucial in designing highly efficient adsorbent for removing heavy- metal ions from aqueous solution. In this paper, a biomass-derived hierarchically porous carbon (HPC) with oxygen- and nitrogen-containing functional groups has been adopted to investigate the adsorption equilibrium and mechanism towards heavy-metal ions (Cu (II), Zn (II), Pb (II), Cd (II), and Cr (III)). It indicates that the adsorption of heavy-metal ions on HPC all fit well with the Langmuir model, but present different adsorption capacity at the same condition. In addition, thermodynamic parameters including Gibbs free energy change and Enthalpy change of these adsorption processes also resemble the variation of the adsorption capacity, implying that the intrinsic characteristics of heavy-metal ions play critical role in the adsorption. Through analyzing the chemical state of the adsorbed heavy-metal ions on HPC, the first hydrolysis constant that is correlated with the hydrolyzing capability of the metal ions, are found to be responsible for the adsorption disparity of HPC towards the five heavy-metal ions since it decides the contact ratio of hydrolyzed heavy-metal ions with HPCs in aqueous solution. Therefore, this work is meaningful in providing a clear and detail insight into the adsorption disparity mechanism of porous carbon towards the removal of heavy-metal ions.