A new 3D unit cell model is developed for homogenization calculation of composites containing randomly dispersed ellipsoid inclusions. The new unit cell is constructed using the Ansys Parameter Design Language (APDL), taking the inclusion volume fraction, inclusion orientation and spatial dispersion as variables. A series of unit cells containing multiple ellipsoids, showing random distributions in particle size and position, were constructed and used for finite element calculation at microscale, the effective modulus of the composites with periodic microstructures, which modeled by the unite cells, were then estimated by homogenization. The influences of particle volume fraction and the particle stiffness on the effective elastic modulus of the composites were examined. The estimated results were compared with different particle volume fractions were calculated, and the calculated data was compared with other classic models.