Thermoelectrics (TEs) are an important class of technologies for harvesting electric power directly from heat sources. To design high performace TE materials, valleytronics has great theoretical potential to maximize a dimensionless figure of merit ZT but has not yet been demonstrated experimentally. Pseudocubic structure approach based on valleytronics paves a new path to manipulate valley degeneracy and anisotoropy with low thermal conductivity caused by short-range lattice distortion. Here, we report a record high ZT = 1.6 around 800 K, realized in totally enviromentally benign Na-doped Cu2ZnSnS4 (CZTS) single crystal. The exceptional performance comes from a high power factor while maintaining intrinsically low thermal conductivity. The results demonstrate that valleytronics is a new strategy and direction in the TE field, which takes advantage of simple material nature tuning without complex techniques.