Selective　laser　sintering(SLS)　process　creates　three-dimensional　objects,　layer-by-layer,　from　powdered　materials.　This　technology　is　based　on　the　thought　of　slicing　computer　model,to　make　3D　parts　with　powdered　materials.　Theoretically　there　are　no　confinement　of　material　types　and　complexity　for　3D　parts　to　be　constructed　The　SLS　process　involves　the　heating　of　the　powder　using　laser　beam.　This　localized　heating　raises　the　temperature　of　the　powder　enough　to　cause　solidification　by　fusion　without　melting.　At　present,　the　materials　are　mainly　non-metal　powders　such　as　paraffin　wax　powder　and　plastics　powders　etc.　Advancements　over　the　past　few　years　have　significantly　improved　to　fabricate　directly　using　metal　powder.　There　are　still　many　problems　that　remain　to　be　solved　The　balling　phenomenon　during　sintering　is　the　major　reason　that　influences　the　superficial　precision　of　sintered　parts,　and　makes　the　part　of　SLS　metallic　powder　can　not　be　satisfied　In　this　paper　authors　try　to　use　Nd:YAG　laser　to　sinter　different　metallic　powders　and　investigate　the　mechanism　of　balling　phenomenon.　The　balling　model　have　been　built　up　to　explain　the　balling　phenomenon.　It　is　concluded　the　energy　input　is　the　key　to　avoid　balling　phenomenon.