We have carried out a detailed investigation of temperature-dependent micro-Raman scattering on In1 − xGaxN films with different Ga compositions (0.06 ≤ χ ≤ 0.91). The observed phonon frequency downshift and linewidth broadening with increasing temperature of A1(LO) and E2(high) modes can be well explained by a model taking into account the contributions of the thermal expansion, the lattice-mismatch-induced strain, and the anharmonic phonon processes. We have elucidated the variation with Ga composition of the contribution of the three- and four-phonon processes in the anharmonic effect. It is found that with increasing Ga composition the three-phonon process increases over the four-phonon process. The variation in the relative contribution from three- and four-processes can be further attributed to the diversification of structural properties and phonon density of states in InGaN.