Electronic structure and optical properties of Ge- doped 6H- SiC (GexSi1- xC) are calculated by ultrasoft pseudopotential technology of total energy- plane wave based on the density functional theory. The formation energy of impurities illustrates that Ge dopants prefer to occupy the substitutional Si sites for lower energy and more stable state. Analysis band structures, density of states and optoelectronic characteristics of 6H-SiC shows that the valence band maximum is determined by C-2p states and the conduction band minimum is occupied by the Si-3p orbital. With more Ge content is incorporated within the structure, the conduction band minimum of GexSi1- xC has moved to lower energy and changes to be determined by Ge- 4p states. Dielectric function illustrates that the electronic transition in Ge0.333Si0.667C which has a maximum Ge content is more simple than in 6H- SiC, and it′ s absorption edge and peaks are red- shifted to lower energy by 0.9 eV and 3.5 eV, respectively.