In　order　to　utilize　energy　fully　a　mathematical　model　of　parallel-feed　multi-effect　evaporation　system　for　conventional　design　was　established.　The　model　included　two　sequential　system-multi-evaporation　system　and　multi-level　preheating　system.　In　this　model,　the　energy-saving　measures,　such　as　condensate　flash,　using　extra　steam　and　thick　liquor　of　each　effect　to　preheat　raw　liquid　were　adopted.　Solid　separation　was　also　considered　in　the　process　of　evaporation.　Material　balance　and　energy　balance　equations　of　complex　parallel-feed　multi-effect　evaporation　system　were　expressed　in　matrix　equation.　By　holding　or　omitting　correlated　block-matrix,　the　matrix　equation　could　be　used　to　describe　the　difference　of　parallel-feed　multi-effect　evaporation　system　with　and　without　solid　separation,　with　and　without　condensate　flash,　with　and　without　preheating　raw　liquid.　The　model　could　also　be　used　in　the　calculation　of　different　effects　to　realize　the　universality　of　the　model.　The　solid-liquid　equilibrium　data　in　the　multi-effect　evaporation　system　with　solid　separation　was　fitted　by　the　intelligent　fitting　method,　which　helped　to　solve　this　problem　by　computer.　The　model　was　solved　by　the　iterative　method　and　matrix　method.　The　result　showed　that　the　model　had　universality.　Using　extra　steam　to　preheat　raw　liquid　and　condensate　flash　were　effective　methods　to　save　energy.　The　steam　consumption　of　four-effect　parallel-feed　evaporation　with　former　energy　saving　methods　was　decreased　by　about　30%　for　evaporation　of　NaOH　solution　containing　NaCl.　The　algorithm　increased　the　convergence　speed　and　stability.