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We examine the penetrability (or fusion cross section) in the influence of a favorable Q value transfer channel. We found that the formula for the cross section cannot be expressed as that given by Broglia et al. Our result does support their idea that the transfer channel gives rise to a large enhancement to the sub-Coulomb heavy ion fusion cross section.Recently, it has become clear that one-dimensional models cannot provide a satisfactory description for a heavy ion fusion cross section at subbarrier energies. ' This has led to the belief that the individual or the internal degrees of freedom of the colliding nuclei may play an important role in the fusion process. One of the interesting suggestions by Broglia et al. 3 is to explain the subbarrier fusion enhancement of the 'Ni+'Ni and 'Ni+'Ge systems by the coupling of nucleon transfer channels with favorable Q values. They are able to fit well the experimental fusion crosssection data by using the following formula:, ), (1) f(a, f ) =-)/2 1 1 . 1 1 r( -, + -,ia )r( -,+ -,a) r( g +ia)r( g + 2ib) 3 1 . 3 1 tion to be c, = [1v'f (et, e2)f (e2, et)] 'rt, c2= vf (et, e2) [1v f(at, e2) f(f2, et) ] = vf (e2, et) [Iv'f (et, e2)f (e2, «) ] 'r2, with v = (X/2) Jp, /0 and (6) where P(E) is the transfer probability and o t and o. 2 are the fusion cross sections for the entrance channel and the transferred channel, respectively.In this paper, we shall examine the validity of Eq. (1) in a quantum mechanical system. %e start with a simple model of a two channel Hamiltonian: