Modified fly ash was prepared through low-temperature roasting method using NaOH as activator. The techniques of Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), energy dispersive X-ray (EDX), X-ray photoelectron spectroscopy (XPS) and the X-ray diffraction (XRD) were introduced to analyze the chemical and physical performance of samples, respectively. It was found that a significant improvements in activity and specific surface area of adsorbent. This work systematically reported the uptake performances of modified materials for single and two mixed toxic cations Pb(II) and Cd(II). The results unveiled that pseudo-second-order model was suitable to analyze the adsorption process. The adsorption process were better fitted by Langmuir model and the maximum uptake capacities were 126.55 and 56.31 mg g-1 for Pb(II) and Cd(II) in single system at 298 K, respectively. Additionally, in mixed solution, the maximum uptake capacity reduced to 120.48 and 36.10 mg g-1 under the same adsorption conditions. Competitive adsorption results demonstrated that adsorption ability was restricted by other metal ions, as while as, the binding affinity of two cations followed the order of Pb(II)>Cd(II). Meanwhile, the co-existed cations as Ca(II), Mg(II) Na(I) and K(I) had antagonistic effects on the uptake of Cd(II) and Pb(II). The results indicate that the modified fly ash was a low-cost and effective adsorbent for the cleaning up metal ions in wastewater, which has a promising application prospect.