InthefieldofComptonscatterimaging,theproblemofhowtogetameaningfulimagefromlarge-scaleobjectisstillnotfullysttled.Thedifficultymainlyliesinthemethodofthecompensationoftheattenuation,Basedontheprincipleofsmall-angleforwardscattering,anewattenuationcorrectionmethodisdeducedinthispaper,wecandistinguishairfromothermaterialsevenitisdeepinsidealarge-scaleobject.Toverifyourmethod,wedesignamodelofaone-meter-longobjectandperformMonteCarlosimulationswithMCNPsoftware.