The polaron confined in a GaAs film deposited on AlxGa1-xAs substrate are investigated in the framework of the fractional-dimensional space approach. We propose a new approach to define the effective length of quantum confinement. Limitations of the definition of original effective well width are discussed. The dimension and the binding energy of a polaron confined in a GaAs film deposited on Al0.3Ga0.7As substrate are obtained and investigated.