In this work, the interphase effects of nanoparticle enhanced polymer composite materials are investigated. Three interphase models based on finite size representative volume element (RVE) are proposed to estimate the effective material properties of nanoparticle-polymer composites, including" (1) The finite Eshelby tensor based shell model, (2) An improved double inclusion model, and (3) A modified Hashin-Shtrikman model. These micromechanics models are employed to analyze the interphase phase effects on the effective material properties of nanoparticle-polymer composites. One crucial factor that influences the strength of nanoparticle enhanced polymer composites is the material properties of the interphase between nanoparticles and the corresponding polymer matrix. These three improved micromechanics models are designed to incorporate interphase effects. Using the interphase models, the authors estimate the effective Young's and shear moduli for a set of four material systems of silica nanoparticle/polyimide composites with the published molecular dynamics simulation data. The micromechanics-based homogenization results are in good agreement with the results of molecular dynamics simulation for all three models. This study shows that the proposed micromechanics interphase models have the capacity to predict effective material properties of nano-particle/polymer composites.