Very　few　studies　have　been　reported　on　the　fundamental　mechanism　analysis　the　augmentation　of　heat　and　mass　transfer　for　the　convection　and　condensation　processes　in　the　slit　finned　tube　heat　exchanger　under　dehumidifying　conditions.　By　developing　a　3D　numerical　model　for　the　condensation　of　the　slit　finned　tube　heat　exchanger　under　dehumidifying　conditions,　the　heat　and　mass　transfer　characteristics　were　investigated　under　different　the　geometrical　and　operational　parameters.　The　models　neglecting　convective　mass　flux　or　neglecting　the　water　vapor　loss　can　greatly　enlarge　the　deviations　of　numerical　results　with　respect　to　experimental　data.　The　synergy　angles　are　smaller　in　the　windward　and　leeward　sides　of　slits　where　the　velocity　field　has　a　better　synergy　with　both　temperature　field　and　the　mass　field.　The　slits　on　the　fin　not　only　increase　the　disturbance　of　fluid　but　continuously　destroy　the　developments　of　thermal　and　mass　concentration　boundary　layers,　greatly　enhancing　the　heat　and　mass　transfer.　The　latent　heat　transfer　is　significantly　greater　than　the　sensible　heat　transfer,　which　accounts　for　71.7%　of　the　total　heat　transfer　rate　when　inlet　velocity　is　1　m　center　dot　s(-1)　and　volume　fraction　of　water　vapor　is　15%.　The　increases　in　the　inlet　velocity,　and　the　volume　fraction　of　water　vapor　can　enhance　the　heat　and　mass　transfer　coefficient　of　wet　flue　gas.　Whereas,　the　increase　in　inlet　velocity　can　reduce　the　difference　of　synergy　for　the　velocity　field　and　the　temperature　or　mass　concentration　gradient　field　of　different　fin　tubes.