Adsorption isotherms of Cu and Cd by coal fly ash were studied through a batch equilibrium experiment and an incubation experiment. Soil pH, available and five chemical speciation of Cu and Cd were also investigated to study the immobilization of Cu and Cd by coal fly ash with application rates of 0.2%, 0.5%, 1% and 2%. The results showed that both the Langmuir and Freundlich equations can be used to describe the sorption of Cu and Cd by the coal fly ash, and maximum sorption amounts of Cu (9.90 mg/g) was higher than that of Cd (9.43 mg/g). Soil pH was significantly increased and available Cu and Cd were decreased with the increasing of application rates of coal fly ash. Meanwhile, the application of coal fly ash significantly decreased the concentrations of exchangeable Cu and Cd and increased the concentrations of Cu and Cd bound to Fe-Mn oxides, which decreased the mobility factors of Cu and Cd, and promoted to the transformation of Cu and Cd from active to inactive fractions. In the soils treated by 2% coal fly ash, soil pH increased 0.44 unit and the concentrations of exchangeable Cu and Cd decreased 35.7% and 35.9% than those in the control after 60 days incubation, respectively. This study indicated that coal fly ash can effectively adsorb Cu and Cd, and reduce available and exchangeable Cu and Cd, which can be applied to immobilize heavy metals in contaminated soils.