[en] The goal of this thesis is the preparation of the Higgs boson search in its di-photon decay at LHC with the ATLAS detector. The issues that have been studied deal with the Higgs→ γγ vertex reconstruction, with the electromagnetic calorimeter and the inner detector, and the di-photon invariant mass resolution. Different simulations of the ATLAS detector and the effects of additional material and of detector misalignments have been studied. Issues concerning the statistical significance calculation have also been discussed and the discovery potential has been evaluated. A part if this thesis is done with CSC data, that use the most recent detector simulation and new reconstruction methods. Every step of the signal and background treatment has been discussed. We finally evaluate that with an integrated luminosity of 10 fb^-1 we will be able to see a Higgs→ γγ signal with a statistical significance of 3 σ. (author)