In this study, response Surface Methodology (RSM) based on Box-Behnken Design (BBD) was employed to analyze the effects of different concentration of cadmium ion, copper ion, zinc ion, chromium ion on the maximum lead-removal rate of rape straw powders in multi-ion designed aqueous solutions. Infrared spectroscopy, scanning electron microscope and energy dispersive spectrometer were used to characterize the rape straw powders before and after the adsorption processes to identify the functional groups and elements which had changed, and therefore, to explore the possible mechanisms of such competitive biosorption. The results showed that the P values of polynomial mode of competitive biosorption were less than 0.0001 (α=0.05), which indicated that the models were significant. The cadmium ion, copper ion, zinc ion, chromium ion all showed their competitive effects on the lead ion-biosorption process. Among them copper ion and chromium ion were more competitive, they can be sorted by competitiveness as follows:copper ion > chromium ion > zinc ion > cadmium ion. The critical groups such as -OH, -C=O, -C-O, -C-H, -CH₂ and amide groups, were exhibited by the Fourier transform infrared spectra, the changes of which suggested that these groups played critical roles during the biosorption process. -CH₃group appeared to be especial during the biosorption process, by making the lead removal rate decrease. The results of Energy Dispersive Spectrometer revealed potassium and sodium ion exchange during the biosorption process. By conclusion, our study suggested that keeping low concentration of copper and chromium ion in solutions was crucial to improve lead ion removal rate of straw powders in multi-ion aqueous solutions.