Mesoporous silica is synthesized by means of sol-gel method in H2SO4 medium and molecular model structure is obtained using annealing simulation with CVFF force field. The characterizations of mesoporous silica are determined by X-ray photoelectron spectroscopy, nitrogen adsorption-desorption and dynamic water vapor sorption analyzer. Surface modified material model are prepared by the attachment of sulfonate grafts to the surface hydroxyl groups. Simulation results of the vapor isotherm are in accordance with the experiments. Mesoporous silica with different surface sulfonate density is simulated and results show water sorption capacity in the low relative humidity increases with higher surface sulfonate density. Analysis and visualization of the molecular behavior at the gas-solid interface can in spire the development of improved synthetic for preparation of surface modified materials with higher surface function groups to enhance the water vapor adsorption capacities.