Abstract: Alkali-activated slag-clay minerals composite cement (AASCM) and ordinary portland cement (OPC) were used to immobilize the simulated radioactive slurry. The leachabilities of Cs⁺, U(Ⅵ) were studied. A two-dimension decay leaching model (T-DLM) applied to predict the leaching behavior of radionuclides was established and optimized, according to Fick’s second law. The leaching behaviors of Cs⁺, U(Ⅵ) were predicted by the T-DLM with non-constant apparent diffusion coefficient, via programmed calculation with MATLAB software. The results indicate that the capacity of AASCM immobilizing Cs⁺, U(Ⅵ) is better than OPC. The cumulative leaching fractions of Cs⁺, from AASCM are less than 1/5 and 1/2 of that from OPC, separately, after leaching for 28 d. The apparent diffusion coefficients of Cs⁺, U(Ⅵ) register as the attenuation trend. While considering the attenuation of apparent diffusion coefficient, the leaching behaviors of Cs⁺, U(Ⅵ) immobilized in OPC and U(Ⅵ) immobilized in AASCM can be predicted well by the T-DLM, but the leaching behavior of Cs⁺ immobilized in AASCM which has stronger ion-exchange and adsorption capacity can not be predicted well.