Optical properties of c- and a-plane wurtzite-InN films with different in-plane strain are investigated by using 8 × 8 k·p method. Taking into account the influence of carrier density, the imaginary parts of ordinary and extraordinary dielectric function of c- and a-plane InN near bandedge are presented. For c-plane InN, the shift of ordinary absorption edge in the case of isotropic in-plane strain in comparison to the unstrained one is very small. For a-plane InN, the splitting between the ordinary and extraordinary components below 1 eV can be modulated with different anisotropic in-plane strain. Furthermore, the difference of splitting between the cases of in-plane strain and strain-free slightly decreases with increasing carrier concentration, which implies the influence of in-plane strain becomes weaker in higher carrier concentration. The spontaneous emission spectrum shows the ratio of peak intensity of y- and z-polarizations increases with enhancement of the splitting. It is considered that the distinct polarization dependent optical anisotropy is expected to be observed in non-polar InN film by appropriately modulating the in-plane strain.