The　separation　properties　of　ion　to　cobalt　and　nickel　in　complexation-precipitation　system　were　studied.　The　relationship　between　metal　ion　concentration　and　pH　value　in　the　complexation-precipitation　systems　of　carbonate　system,　ammonia　system　and　carbonate-ammonia　system　was　simulated　by　the　thermodynamic　calculation.　Combined　with　the　experiments,　the　carbonate-ammonia　system　was　considered　as　the　best　ion-removal　system,　which　can　guarantee　a　high　iron　removal　efficiency,　small　amount　of　cobalt,　nickel　lost,　and　is　conducive　to　the　subsequent　separation　of　cobalt　and　nickel.　The　results　show　that　the　optimal　ion-removal　conditions　in　carbonate-ammonia　system　are　determined　as　follows:　(CoNi)/　Fe3+　concentration　ratio　of　1.5-2.5;　ammonia　concentration　of　1　mol/L;　Na2CO3　concentration　of　0.01　mol/L;　pH　value　of　4.0.　Under　this　condition　of　(CoNi)/Fe3+=2.5,　the　ion-removal　rate　is　over　99%,　the　cobalt　loss　rate　is　about　11.4%,　and　the　nickel　loss　rate　is　10.6%.　This　ion-removal　method　has　the　advantages　of　high　iron　removal　efficiency,　favorable　filtration　performance　and　good　application　prospect.