Abstract: A novel nano-magnesium hydroxide powder was chosen as a dispersion phase material and mixed with nitrile rubber(NBR), ethylene-propylene-diene mischpolymer (EPDM), styrene-butadiene rubber(SBR) and silicone rubber(SiR) to make a series of composites. By scanning electronic microscopy (SEM), transmission electronic microscopy (TEM) and Payne effect, the dispersion morphology and network structure of the composites were investigated in detail. The experimental results indicate that viscosity and surface energy of the matrix play very important roles in dispersion and network forming of nano-powder in rubber. The higher the viscosity or surface energy (EPDM, NBR) of the matrix, the finer the dispersion of nano-powder, and the more easily the network forms. The network is flexible due to the large proportion macromolecules involved. But in the rubber (SiR) with low viscosity and surface energy, there exist isolated agglomerates, not forming network in the low loading condition, while in the high loading condition the rigid network is formed by direct contacting of agglomerates, and the proportion of the macromolecule in the network is low. Traditional models can not describe the effect of main factors on the force on the agglomerates; a new modified model is proposed to introduce the effect of surface energy of the matrix.