With the development of environmental compatibility, thermoelectric materials are required high performance coupled with environmental friendly elements. Therefore, GeTe materials have been widely studied as an ideal alternative to PbTe alloys owing to their non-toxic characteristics. In recent years, the doping method is considered to be the main way. Due to the limitations of single element doping, double elements doping have become the leading ways. Meanwhile, the Pb elements have gradually replaced by Sb, Bi and etc. This paper has introduced the crystal structures as well as band structures. Moreover, the optimization methods have been summarized as well, including carrier concentration optimization, energy band engineering and structure control. Nowadays, the GeTe thermoelectric devices are mainly p-type legs, while the n-type of GeTe-based alloys are required for further research. Furthermore, the fracture of the interface in thermoelectric devices caused by phase transition should be solved in the near future.