Abstract: An algorithm for the automatic generation of 2D representative volume element (RVE) of nano-particle reinforced composites is developed by using Monte-Carlo method. The bilinear cohesive zone model was adopted to evaluate the weak interface traction and separation distance. The macroscopic mechanical behavior of nano TiO₂ particle reinforced epoxy composite was simulated by using ABAQUS software, and the validity of model is demonstrated by comparison of test results and simulation results. The effects of TiO₂ particle mass fraction and particle size on composite macroscopic effective modulus, and the progressive damage process of composites, were discussed under weak interface condition. The results show that the Young’s modulus and fracture elongation of composite increase gradually with the increasing of mass fraction of TiO₂ particle, while the yield strength decreases. Under the same mass fraction of particulate, the total length of interfacial unit between particulates and matrix, and the fracture elongation of composite, were gradually reduced with the increasing of TiO₂ particle size.