A semi-empirical model was developed to predict the breakthrough curves of moisture adsorption on silica gel under different operating conditions. The model requires only the basic physical and transfer properties of the flowing gas stream. Experimental breakthrough curves were determined in this study for correlating some model parameters. These dynamic experiments were carried out with different values of the gas velocity, the inlet humidity, and the properties of the adsorbent. The breakthrough curves of the modified silica gel with neutron flux in a previous study were used to verify the proposed model. It is feasible to develop a single adsorption model to simulate the fixed-bed breakthrough curves for original and modified silica gels. The results show that the complex breakthrough curves can be predicted and are in very good agreement with the experimental data.