Abstract:Physics experiments on large scale uniform and non-uniform granular mixtures avalanche were carried out and the results proved that internal cause of SOC effect was most probably the structure characteristics of the system but not the size of granular or the scale of system. Furthermore, the stress transmission and stress distribution of uniform and non-uniform granular mixtures were simulated with discrete element method. According to the contrast between uniform and non uniform granular mixtures from three parameters of Shannon entropy, porosity and coordination number,it was found that the stuffing of granular matter in the non uniform granular system is more sufficient, so the system is more stable and it can show SOC. Meanwhile, there is no distinct difference of fractal dimension between the uniform and non uniform granular mixtures and thus the fractal could not be thought as the criterion of SOC.