Most　areas　of　Caofeidian　(Tangshan　Caofeidian　New　District　in　Hebei　Province,　China)　were　formed　by　land　reclamation,　where　the　dredger　fill　has　a　high　water　content　and　a　high　salt　content.　The　solidification　of　Caofeidian＇s　dredger　fill　is　difficult　because　of　salinisation,　as　well　as　environmental　and　economic　factors.　This　article　proposes　a　composite　slag　solidifying　agent.　The　optimal　proportion　of　various　additives　was　determined　by　an　unconfined　compression　test　and　orthogonal　design.　Next,　a　microanalysis　was　carried　out　by　SEM　and　XRD　tests　to　characterise　the　solidification　mechanism　of　the　composite　slag　solidifying　agent.　The　results　reveal　that　the　composite　slag　solidifying　agent　can　substantially　improve　the　unconfined　compressive　strength　of　Caofeidian＇s　saline　dredger　fill　by　imparting　a　good　microstructure:　a　compact　overall　structure　was　obtained　and　few　voids　were　observed　in　the　solidified　soil.　The　optimal　proportion　was　determined　as　10%　slag　+　1.0%　quicklime　+　0.8%　sodium　silicate　+　1.5%　gypsum　powder.　In　addition,　the　composite　slag　solidifying　agent　can　effectively　reduce　the　content　of　soluble　salts　in　saline　dredger　fill　and　substantially　improve　the　engineering　characteristics　of　solidified　soil.