Abstract: The phenomenon that the gas dissolved in water can be adsorbed and accumulated on the hydrophobic surface is discovered by condensed matter physics. Thus, when the distance between the hydrophobic objects is small enough, the gases adsorbed on the hydrophobic surfaces will connect each other and form nanobubble bridges. The nanobubble bridges cause hydrophobic attraction. However, the formation/disappearance process and the morphology of nanobubble bridges have not been provided in academe of mechanics. In this article, the interactions of a pair of graphene in liquid water with and without gas phase are studied using molecular simulation. The changes of structural phase diagram and potential of mean force of the system, the density distribution of gas and water were analyzed. The results show that the hydrophobic attraction of two pieces of graphenes is really caused by the nanobubble bridge. When the distance between the pair of graphenes is less then approximate 0.5 nm, hydrophobic attraction is led by vacuum nanobubble bridge no matter with or without gas phase in water. When their distance is greater than approximate 0.5 nm, the hydrophobic attraction without gas in water is led by the nanobubble bridge of vapor, and the hydrophobic attraction with gas in water is led by the nanobubble bridge of the gas.