The modeling of structural and thermodynamic properties of complex oxides with orthorhombic perovskite structure CaZrO3, CaTiO3 and CaSnO3 was performed by means of atomistic computer pair potentials method in ionic approximation. The results of calculations for the structural properties are in a good agreement with experimental data and previous calculations, while the calculated values of bulk modules are overestimated. The calculated entropy values for the room temperature are in a good agreement with available experimental data for CaTiO3 and CaZrO3. For the first time the entropy was calculated in the temperature range 300 —1800 K for all three perovskites and the results are in a satisfactory agreement with experimental data for CaTiO3. The formation energies of isolated intrinsic point defects in these crystals were calculated by using Mott-Littleton approximation. For all three perovskite structures the most energetically favorable appears to be a Ca—O Schottky defect. The solution energies of the isovalent tetravalent substitutions (Zr4+, Ti4+, Sn4+, Hf4+, U4+, Th4+) in CaZrO3, CaTiO3, CaSnO3 were also found in the approximation of infinite dilution. The enthalpies of mixing of the continuous binary solid solutions CaZrO3 — CaTiO3, CaTiO3 — CaSnO3, CaSnO3 — CaZrO3 were obtained by using of simple mixture model. The solution of the isolated trivalent dopants (Sc3+, Y3+, Cr3+, Fe3+, La3+) and the tetravalent (Hf4+, U4+, Th4+) dopants were considered both in A and B (A = Ca, B = Zr, Ti, Sn) sites of all three perov skites. According to these calculations, the most energetically favorable mechanism of incorporation of the trivalent dopants is the self-compensation at simultaneous substitutions on A and B sites. The most favorable way of incorporation of the tetravalent ions M4+ is an isovalent substitution of B4+ ion.