There are different approaches for investigating the force as well as the gravity. Newton emphasized the mathematical meaning of gravity. Einstein’s gravity is geometry. The physical exploring for gravity is still on the way. Le Sage investigated the nature of gravity, but his theory has many defects. This paper gives out a physical chemistry approach for the nature of force, which bases on gravitons’ reaction by introducing the concepts of Gibbs free energy change and holographic screen. The change of the Gibbs free energy results in the imbalance on the two sides of the holographic screen, it is the force. The change of force as the distance depends on the distribution of gravitons. For the solar system, the graviton gas distributes in the centre-radical pattern, so the inverse-square law is applicable. But in the galaxies, the distribution of the graviton gas is not in center-radical, therefore the acceleration is just inversely proportional to the distance (not square of distance), which is equivalent to the centripetal force. The flatness of the rotation curve can be explained without dark matter.