Experimental results show that gas dissolved in water can be adsorbed and accumulated on hydrophobic surface. There are two formations of adsorbed gas, nanobubbles and micro pancakes. Classical theory can't explain their stable existence. In this paper, molecular dynamics simulation was used to study the adsorption and agglomeration of gas. It is found that there exist a gas-liquid mixed layer coated on the adsorbed gas. The shape and characteristics of the mixed layer were studied and analyzed. It was found that the viscosity of gas-liquid mixture was greater than that of water and it inhibits gas diffusion.