Wurtzite InGaN solid solutions have been designed via indium’s incorporation into GaN crystal. In this work, the electronic structure and optical properties are theoretically investigated in order to improve the optoelectronic performance of GaN semiconducting material. Not only the lattice parameters of In_xGa_1-xN (x = 0, 0.25, 0.5, 0.75 and 1), but also their optical properties have been delved into. It is found that the optical wavelength range was enlarged when alloying GaN with indium and the increased proportion of indium makes absorption curves shift towards lower energies, which covers the whole visible light region. Because of the excellent optoelectronic performance of these materials, a lot of new applications can be expected in the near future.