We study the combined effects of hydrostatic pressure, aluminum concentration, well width, and temperature on linear and nonlinear optical absorption spectrum inGaAs/Ga1−xAlxAs quantum well under the applied magnetic field via investigating the phonon-assisted cyclotron resonance (PACR) effect. Our result shows that the optical absorption behaviors are affected strongly by hydrostatic pressure, aluminum concentration, temperature and well width. Besides, the present work discovers a clear monotonic behavior of the resonant peaks and the half-width as functions of the pressure, concentration, temperature or well width in both one- and two-photon absorption processes.