Through the characterization of fly ash samples, the speciation and physicochemical properties related to the adsorption of lead and cadmium were explored, and the static adsorption experiments of lead and cadmium in water were carried out. Based on the experimental data, adsorption isotherm was modeled with Langmuir, Freundlich, and Tenkin equations. The adsorption equilibrium properties of lead and cadmium were analyzed, the adsorption kinetics was studied to describe the adsorption process, and the potential adsorption rate control steps and adsorption mechanism were studied. The results showed that the content of unburned carbon in fly ash had a certain influence on the adsorption of lead and cadmium, and the Al—O/Si—O or Si—O—Si/Si—O—Al functional groups in the cyclic silicate on the surface of fly ash played a major role in the adsorption of lead and cadmium. Langmuir isotherm equation presented better fitting result, indicating that fly ash surface was uniform, and the adsorption of lead and cadmium in aqueous solution had both physical and chemical adsorption, which belonged to monolayer adsorption. The maximum adsorption capacity of fly ash for lead and cadmium at 25 ℃ in water was 69.930 1 mg/g and 36.904 0 mg/g, respectively. The pseudo-second-order kinetic model could describe the adsorption process more accurately, showing that lead and cadmium adsorption on fly ash surface was controlled dominantly by chemical adsorption.