The linear and nonlinear optical absorptions in square tangent quantum well were investigated. Analytic forms of the linear and third-order nonlinear optical absorption coefficients were derived using the compact density matrix approach method. Based on this model, the numerical results were presented for a typical AlGaAs/GaAs square tangent quantum well. The calculated results show that the shape of quantum well and incident optical intensity have great influence on the optical absorption coefficients in square tangent quantum well.