According　to　the　principle　of　manufacturing　of　fused　silica　composites　reinforced　by　short　carbon　fibers,　a　micro-mechanical　model　was　developed　to　investigate　the　mechanical　properties　of　the　composites.　The　composites　consisted　of　a　fused　silica　matrix,　Si3N4　grains　and　short　carbon　fibers.　It　was　assumed　that　the　composites　have　a　periodic　microstructure.　The　transverse　Young＇s　modulus,　shear　modulus　and　Poisson　ratio　of　the　composites　were　calculated　by　the　two-scale　expansion　method.　The　numerical　results　agreed　with　the　experimental　data.　The　numerical　results　demonstrate　that　all　the　effective　stiffness　coefficients,　the　Young＇s　modulus　and　the　shear　modulus　increase　at　first　and　then　decrease　with　the　increase　of　the　content　of　the　carbon　fiber.　They　reach　a　maximum　when　the　fiber＇s　volume　fraction　is　30%.　The　composites　have　optimal　mechanical　properties　at　a　sintering　temperature　of　1400C　and　the　fiber　volume　fraction　of　30%.