Perovskite-type Ca1−xYbxMn0.98Nb0.02O3 (x = 0, 0.02, 0.05, 0.08, and 0.1) thermoelectric materials were synthesized by a solid-state reaction technique. The dopant-level dependence of lattice parameter, the correlation of crystallographic structures and the high temperature properties of these codoped CaMnO3 systems were investigated. The results show that codoping in A and B-sites of the perovskite structure improves the ZT value noticeably rather than the single doping. This is driven by the compromise among carrier concentration, structural distortion, and phonon impediment. The increase of Yb doping leads to higher phonon impediment and consequently reduces thermal conductivity. In this codoping system, the effective doping content is x = 0.05 in order to reduce the thermal conductivity. The sample with nominal composition of Ca0.95Yb0.05Mn0.98Nb0.02O3 reaches the highest ZT of 0.13 at 973 K, which is almost 18% higher than that of the single-doped CaMn0.98Nb0.02O3.