The discrete element method is used to research the distribution of forces within the two-dimensional granular system under gravity. The force chains among the particles are generated according to the magnitudes of the forces. Then the simulation results are compared with the well-known q-model，α-model and experimental results obtained through the photoelastic test under the same conditions. According to the computational solution， we conclude that the simulation results are similar to the experimental results are some what different from the two probability models. In addition， we also obtained that the probability distribution of the force is very uneven. The probability of the large force decays exponentially and the distribution of the force chains takes on a fractal character.