Two-photon decay of the Higgs boson H → γγ and its reverse process γγ →H are　important processes in detecting Higgs boson which plays a fundamental role in the　Standard Model of electroweak interaction. We calculate the QCD corrections to these　processes for all mass ranges of the Higgs boson without any constraint for the top quark　mass. For a heavy Higgs boson (mh > mt), the QCD corrections become very large　(50-100%), while for a lighter one (toh < mt), the corrections are negligible.