Abstract: The digital image processing technology was used to obtain the shape of organoclay nanoparticles and distribution of the nanoparticles on PP matrix from the SEM image of PP/organoclay particle-reinforced nanocomposite. Then a 2D RVE(representative volume element)model could fully reflecting the microstructure of the composites was built.The stretching simulation process was carried out by finite element method, the elastic modulus of the composite was predicted by calculating the average stress and strain, and the distribution of the stress and strain in the composite were also analyzed. The results show that the calculation results fit well with the experiment ones. The method through the digital image processing and finite element analysis is reliable for predicting elastic modulus of particle-reinforced polymer nanocomposite.