An　amphoteric　lignin　flocculant　LSDC　was　prepared　by　graft　and　Mannich　reaction　with　calcium　lignosulfonate　as　raw　material.　The　preparation　conditions　were　optimized　and　LSDC　was　characterized　by　Py-GC-MS.　The　results　of　applying　LSDC　to　the　bio-active　sludge　showed　that　ISDC　can　speed　up　the　sedimentation　rate,　decrease　moisture　content　and　specific　filtration　resistance　of　the　sludge.