  We show that the controversies on the gauge dependence and the infrared
singularity emerged in the generalized factorization approach for nonleptonic
heavy meson decays within the framework of the operator product expansion can
be resolved by perturbative QCD factorization theorem. Gauge invariance of the
decay amplitude is maintained under radiative corrections by assuming on-shell
external quarks. For on-shell external quarks, infrared poles in radiative
corrections have to be extracted using the dimensional regularization. These
poles, signifying nonperturbative dynamics of a decay process, are absorbed
into bound-state wave functions. Various large logarithms produced in radiative
corrections are summed to all orders into the Wilson and Sudakov evolution
factors. The remaining finite part gives a hard subamplitude. A decay rate is
then factorized into a convolution of the hard subamplitude, the Wilson
coefficient, and the Sudakov factor with the bound-state wave functions, all of
which are well-defined and gauge invariant.
