This　study　focuses　on　the　design　of　Sialon-TiB2-AlN　composite　ceramics　with　thermal　expansion　coefficients　matched　to　that　of　cubic　boron　nitride　(cBN),　used　as　binders　to　synthesize　PcBN　composites　in　situ　under　conditions　of　ultra-high　pressure　(5.5　GPa)　and　high　temperature　(1400　degrees　C-1600　degrees　C).　The　effects　of　sintering　temperature　and　Y2O3　content　on　the　phase　composition,　microstructure,　and　mechanical　properties　of　PcBN　composites　were　systematically　investigated.　The　results　show　that　the　phase　compositions　of　the　composites　with　different　sintering　temperatures　are　the　same.　A　moderate　addition　of　Y2O3　enhances　the　formation　of　Sialon　within　the　system　and　promotes　an　increase　in　its　aspect　ratio.　When　the　Y2O3　content　is　2%,　both　long　columnar　Sialon　and　needle-like　(or　plate-like)　TiB2　coexist,　with　the　aspect　ratio　of　Sialon　ranging　from　4:1　to　5:1.　At　this　composition,　the　interface　bonding　is　optimal.　Under　these　conditions,　the　Polycrystalline　cubic　boron　nitride　(PcBN)　composite　exhibits　the　best　overall　performance,　achieving　flexural　strength　of　990.72　MPa,　hardness　of　28.49　GPa,　fracture　toughness　of　7.8　MPam(1)/(2),　and　a　maximum　wear　ratio　of　1602.