The　synthesis　of　high　ductility　geopolymer　composites　using　excavated　natural　clay　is　an　economical　and　environmentally　friendly　method　to　realize　the　utilization　of　excavated　natural　clay.　This　paper　presents　an　experimental　research　on　the　flexural　properties　and　pore　structure　characteristics　of　engineered　geopolymer　composites　(EGC)　prepared　by　calcined　natural　clay.　The　EGC　with　different　slag　and　fiber　contents　were　prepared　and　the　four-point　bending　tests　were　conducted　on　the　EGC.　The　effect　of　slag　and　fiber　content　on　the　flexural　strength,　flexural　deflection　and　flexural　toughness　were　discussed.　The　microscopic　pore　structure　characteristics　of　EGC　were　further　analyzed.　The　optimal　mixture　ratio　of　calcined　clay-based　EGC　with　the　highest　flexural　toughness　was　proposed.　The　results　show　that　fiber　can　significantly　enhance　the　flexural　properties　and　cracking　control　ability　of　EGC.　The　ultimate　flexural　strength,　flexural　deflection,　flexural　strengthening　index　and　flexural　toughness　of　EGC　all　increase　with　increasing　fiber　content.　The　results　also　show　the　addition　of　10.0　%　slag　can　increase　the　flexural　strength　and　flexural　toughness,　while　excessive　slag　content　reduces　the　flexural　properties.　The　EGC　with　10.0　%　slag　content　and　2.5　%　fiber　content　exhibits　excellent　flexural　properties　and　cracking　control　ability.　The　ultimate　flexural　strength　and　flexural　toughness　index　reach　9.75　MPa　and　486.11,　showing　the　highest　flexural　toughness.