The band structure of InGaAs strained quantum wells are investigated using 8×8 Luttinger-Kohn Hamiltonian including conduction band, heavy hole, light hole, spin-orbit splitting and strain effects. The energy dispersion curves of conduction band and valence band, the material gain spectra of TE and TM mode are given, respectively. The variation of peak gain with carrier density, temperature, well width, and Indium composition of InGaAs are calculated. The calculations show that the higher the In composition of InGaAs and the thicker the well, the longer the emitting wavelength are. The higher carrier density and higher In composition lead to the higher peak gain.