For　the　selection　a　safe　area　during　landing　on　asteroid,　this　article　proposes　an　algorithm　of　selecting　safe　landing　area　based　on　binaryzation　combined　with　morphology.　First,　it　provides　a　new　binary　algorithm　for　highlighting　the　shadow　area　and　the　lighting　area.　Second,　in　order　to　dilate　the　shadow　area　and　the　lighting　area　by　Using　of　algorithm　of　dilatation　of　morphology.　Last,　choosing　the　bigger　area　which　is　not　dilated　as　the　final　safe　landing　area.　The　algorithm　raised　in　the　article　is　tested　and　proved　by　a　group　images　of　asteroid　topography.