Cadmium　sulfide　(CdS)　exhibits　remarkable　light　absorption　capabilities　and　is　widely　employed　in　photocatalytic　reduction　of　CO2.　Nevertheless,　the　crystal　facet　effects　on　the　micro-scale　mechanisms　governing　CO2　conversion　on　CdS　remain　elusive.　This　study　theoretically　investigates　the　electronic　properties　of　hexagonal-phase　(101),　(001),　and　cubic-phase　(111)　CdS　surfaces　modified　with　diethylenetriamine　(DETA).　From　a　microscopic　viewpoint,　it　elucidates　the　unique　bonding　characteristics　of　CO2　on　different　exposed　facets　of　DETA/CdS　and　the　formation　mechanisms　leading　to　products　such　as　CO,　HCOOH,　CH2O,　CH3OH,　and　CH4.　Our　findings　reveal　that　the　DETA/CdS(101)　surface　is　the　most　stable,　effectively　adsorbing　hydrogen　and　CO2　at　varied　Cd　sites　with　a　high　selectivity　towards　CO　production,　thereby　showing　promise　for　syngas　generation,　albeit　with　potential　yields　of　formic　acid　and　methane.　Conversely,　DETA/CdS(001)　and　(111)　primarily　facilitate　the　reduction　of　CO2　to　CH4.　These　discoveries　offer　theoretical　insights　into　photochemical　experiments　involving　CO2　reduction　on　CdS,　shedding　light　on　the　influence　of　crystal　facets　on　reaction　pathways.