The discovery of band convergence has opened an effective avenue for significantly enhancing thermo-electric performance of SnTe,while alloying CdTe in SnTe is evidenced efficient for improving the valley degeneracy.However,the thermoelectric transport properties are limited due to the low solubility of CdTe in SnTe (～3％).Inspired by the improvement of dimensionless figure of merit zT in Cu or Se-doped SnTe,investigating the effect of Cu2Se on the electronic and phonon transport properties of SnTe-CdTe alloys is highly desired.Traditionally,improving the quality factor can trigger an increase of the potential of a compound for higher zT,which is of importance for design of thermoelectric materials.Here,alloyed 3％ Cu2Se in SnTe-3％CdTe system enables an increased peak zT,which is attributed by the optimization of electronic performance (～21 μW cm-1 K-2 at 800 K),as well as the decreased lattice thermal conductivity owing to the enhanced mass and strain fluctuations.More importantly,alloying Cu2Se not only improves the quality factor from ～0.25 to ～0.45,resulting in a higher maximum potential zT,but also effectively preserves the Fermi energy in a relative optimized level.The current findings demonstrate the role of Cu2Se for manipulating thermoelectrics in SnTe.