CaAl2 Si2 O8-Al2O3-CaAl12 O19( CAS2-Al2O3-CA6) composite was synthesized through reaction sintering alumina and bauxite reducing slag.The CAS2-Al2O3-CA6 composite was mainly composed of α-Al2O3,CAS2,and CA6.Gehlenite( Ca2Al2 SiO7,C2AS) phase was effectively transformed to CAS2 and CA6through high-temperature reaction sintering under weak oxidizing atmosphere at 1400 ℃ for 4h.SEM( scanning electron microscopy) and EDS( energy dispersive spectroscopy) analysis indicated that black and needle-shaped Al2O3,rhombic or irregular polygonal-shaped Fe Al2O4,and glassy phase Ca2Al2 SiO7disappeared after the reaction sintering.The light gray and flaky hexagon crystals of Ca Al12O19(10μm) and the grainy particles of Al2O3( 2-7μm) were observed in the CAS2-Al2O3-CA6 composite.The gray crystals of CAS2 act as the binding phase and are distributed around CA6 and Al2O3.CAS2-Al2O3-CA6 composite exhibits high refractoriness and service temperature,which are 1650 ℃ and 1450 ℃,respectively.Reaction sintering of alumina and bauxite reducing slag is a feasible method for the synthesis of CAS2-Al2O3-CA6 composite.