In this paper, the biochar prepared by pyrolysis biomass of Water Hyacinth were used as adsorption materials. The effects of initial concentration, adsorption temperature and electrolyte concentration on the adsorption process were analyzed. The adsorption effect of biochar prepared from the stem and root parts of biomass on Cd²⁺ in solution was investigated, and the interaction between leaching rule of alkali (earth) metal K⁺, Mg²⁺, Ca²⁺ and adsorption of heavy metal ions in the process of adsorption was studied. The results showed that the biochar prepared by pyrolysis of stem biomass (SBC) has a richer pore structure. Compared with the biochar prepared by root biomass (RBC), the specific surface area and pore volume of SBC increased by 25.85% and 27.91% respectively. This phenomenon indicated that SBC had a stronger adsorption effect than RBC. At 25ºC, the maximum adsorption capacity of RBC and SBC for Cd²⁺ was 77.20 mg g^-1 and 87.20 mg g^-1, respectively. Isothermal adsorption experiments and ionic strength experiments showed that the increase of temperature could promote the adsorption of Cd²⁺ by biochar. The adsorption process has a high degree of fitting with the Langmiur model, as well as the pseudo-second-order model. The adsorption sites were normally on the inner and outer surfaces of biochar, and the adsorption process was multi-molecular layer adsorption. In addition, the adsorption of Cd²⁺ by biochar had a correlation with the leaching of alkali (earth) metal in the system. In the adsorption process, the leaching of alkali (earth) metals was affected by the initial concentration of Cd²⁺ in the solution, and SBC leached more alkali (earth) metals than RBC, which proved that SBC has more active sites and can replace heavy metals in the solution. This study proved that Water Hyacinth biochar owned characteristics of high recovery and low economic cost, which showed good adsorption to Cd²⁺ polluted wastewater and was feasible as a heavy metal adsorption material.