The zincblende InxGa1−xN alloys are studied by numerical analysis based on first-principles calculations. A 64-atom supercell is used to model these alloys. Our results indicate that the ternary InxGa1−xN alloys have an average band gap bowing parameter of 2.08 eV. The simulation results also suggest that the composition-dependent bowing parameter of the ternary InxGa1−xN alloys can be expressed by a third-order polynomial equation, b(x) = −4.7422 x3 + 6.9592 x2 − 2.3136 x + 2.1301 (eV).