An　automatic　method　is　proposed　to　solve　the　registration　problem,　which　aligns　a　single　2D　fluoroscopic　image　to　a　3D　image　volume　without　demanding　any　additional　media　like　calibration　plate　or　user　interactions.　First,　a　mathematic　projection　model　is　designed　which　can　reduce　the　influence　of　projection　distortion　on　parameter　optimization　and　improve　the　registration　accuracy.　Then,　a　two　stage　optimization　method　is　proposed,　which　enables　a　robust　registration　in　a　wide　parameter　space.　Furthermore,　an　automatic　registration　framework　is　proposed　based　on　the　Fourier-Mellin　robust　image　comparison　descriptor.　Experimental　results　show　that　the　registration　method　has　a　high　accuracy　with　average　rotation　error　of　0.6　degree　and　average　translation　error　of　1.4　mm.　Copy　Right　by　Hight　Technology　Letters　Press.