Using banana straw biochar as the base, an iron-manganese loaded biochar was prepared by impregnation modification method to adsorb Cd2+. Response surface methodology was used to optimize the preparation conditions of modified biochar. Under the best preparation conditions, the predicted adsorption capacity of Fe-Mn modified biochar for Cd2+ was 235.64 mg·g-1, and the actual adsorption capacity was 221.03 mg·g-1, with a relative deviation of 6.2%. SEM-EDS, XRD and FTIR analysis showed that the modified biochar was successfully loaded with Fe and Mn. The main adsorption mechanisms for Cd2+ were ion exchange, complexation precipitation, mineral precipitation and cation -π interaction. The adsorption of Cd2+ by Fe-Mn modified biochar accords with Langmuir model and quasi-second-order kinetic equation, indicating that the adsorption process is monolayer adsorption and chemisorption.