In　December　2015,　the　Beijing-Tianjin-Hebei　(BTH)　region　experienced　several　episodes　of　heavy　air　pollution.　Beijing　municipal　government　therefore　issued　2　red　alerts　on　December　7　and　19,　respectively,　and　also　implemented　emergency　control　measures　to　alleviate　the　negative　effects　of　pollution.　It　is　estimated　that　the　heavy　pollutions　in　2　red　alert　periods　in　Beijing　were　due　mainly　to　the　accumulation　of　air　pollutants　from　local　emission　sources　and　the　transboundary　transport　of　pollutants　from　surrounding　areas.　The　collected　meteorological　and　PM2.5　data　indicate　that　the　severity　of　air　pollutions　were　enlarged　by　the　poor　meteorological　conditions　along　with　lower　mixing　layer　height.　In　this　study,　the　WRF-CAMx　modeling　system　was　utilized　not　only　for　analyzing　the　contributions　of　PM2.5　from　different　sources,　but　also　for　quantitatively　assessing　the　effects　of　implementing　various　emergency　control　measures　on　PM2.5　pollution　control　during　the　red　alert　periods.　The　modeling　results　show　that　local　emissions　were　the　most　dominant　contributors　(64.8%-83.5%)　among　all　emission　sources,　while　the　main　external　contributions　came　from　the　city　of　Baoding　(3.4%-9.3%).　In　addition,　among　5　different　emission　source　categories,　coal　and　traffic　were　the　two　dominant　contributors　to　PM2.5　concentration　in　urban　area　of　Beijing.　Then　four　pollution　control　scenarios　were　designed　particularly　to　investigate　the　effectiveness　of　the　emergency　control　measures,　and　the　results　show　that,　generally　these　emergency　control　measures　have　positive　effects　on　air　pollution　reduction.　In　particular,　restrictive　measures　of　traffic　volume　control　and　industrial　activity　shutdown/suspension　have　been　found　as　the　most　effective　measures　in　comparison　to　other　emergency　control　measures.　It　is　recommended　that　such　effective　measures　should　be　considered　to　implement　when　next　time　similar　heavy　air　pollutions　occur　in　the　city　of　Beijing.