A mechanical response of a brittle material under shear loading was numerically investigated within the concept of a multilevel approach. The material was considered to have hierarchical porous structure with a plastic filler. A two-dimensional model of mechanical behavior of ceramic composites with different porosity and filler-containing pore fraction was developed on the basis of a discrete medium approach and a movable cellular automaton method. Model calculations were carried out for a composite filled with plastic material with elastic and strength properties of cortical bone. A loading diagram of the filler was described by bilinear hardening. Ceramic composite matrix had mechanical properties of nanocrystalline ZrO2 (Y2O3) (yttria-stabilized zirconia) with bimodal distribution function of pore sizes and an average pore size greater than average grain size. Variations of ceramic porosity were between 0.225 and 0.345, and filler-containing pore fraction — between 0 and 1. The value of porosity corresponding to pores with a size of the first peak of the distribution function was 0.085. Numerical calculations provided the basis for an analytical evaluation of dependencies of shear strength and elastic modulus on total porosity and fraction of pores with a filler.