By using the compact density matrix approach and displacement harmonic variant and numerical calculation methods,the linear and nonlinear intersubband refractive index changes(RICs) in a semi-parabolic quantum well with applied electric field were investigated in detail.Numerical calculations on GaAs were performed for the dependence of RIC on the incident optical intensity,the frequency of confined potential of the semi-parabolic quantum well and the strength of applied electric field.Results reveal that the RICs in the semi-parabolic quantum well system sensitively depend on these factors.