With the imminent start of the ATLAS data taking in 2007, the well considered strategy is necessary for the good understanding of the detector performance from in situ calibration and the realistic estimation of the Standard Model background. These are urgent issues for the new physics discovery channels especially for the SUSY searches in the early data taking of LHC run. The talk starts with the brief overview of the ATLAS detector and the calibration commissioning, then the realistic background estimation using real data and the matrix element calculation continues. Finally the newly obtained SUSY discovery potential with newly estimated backgrounds is presented.

PACS numbers: 11.30.Pb, 14.80.Ly, 13.85.--t