In this paper، the optical properties of the quantum double folded potential well in the terahertz frequency region are investigated. The Schrö dinger equation is solved and using the obtained wave functions، the standard density matrix and the iterative method the refractive index and the absorption coefficient in the first order is calculated and investigated. The results show that for the proper choice of the parameters، the maximum absorption could lie in the terahertz range that is appropriate for use in terahertz devices. Furthermore، the effects of small potential disturbances on frequency absorption coefficient and thus the stability of the system are studied. The results of these calculations show that for small fluctuations the maximum absorption remains in the terahertz range، but by increasing the disorder، this maximum gradually increased and move toward infrared frequencies.