In this work, we fabricate perovskite-type Ca_1-x-yLa_xSr_yMnO₃ thermoelectric materials using co-precipitation method, followed by cold pressing and hot sintering. The La/Sr dual doping modifies chemical composition and bonding properties of CaMnO₃, resulting in improved electrical transport properties with tunable carrier concentration, carrier mobility and effective mass. Meanwhile, the phonon transport properties are also influenced, reflected by the reduced lattice thermal conductivity of Ca_1-x-yLa_xSr_yMnO₃. As a result, Ca_0.94La_0.02Sr_0.04MnO₃ shows significantly enhanced power factor up to 374 μW·m^-1·K^-2 and figure of merit up to ∼0.22 at 973 K, which is ∼144% higher than those of pristine CaMnO₃. This study rationalizes a potential strategy to improve the thermoelectric performance of CaMnO₃-based materials.