Acetylene　semi-hydrogenation　is　a　vital　process　where　the　utilization　of　supported　isolated　Pd　atoms　as　catalytic　active　sites　is　promising　due　to　their　unique　reactivity　and　metal　atom　efficacy.　In　particular,　doping　Pd　single　atoms　at　different　sites　on　metal-oxide　surfaces　provides　an　opportunity　to　regulate　their　local　coordination　environments　and　modulate　their　electronic　and　catalytic　properties.　In　this　study,　we　conduct　extensive　density　functional　theory　calculations　to　investigate　the　influence　of　single　Pd　atom　coordination　environments　and　surface　properties　on　the　activity　and　selectivity　of　Pd-1/TiO2　catalysts　for　acetylene　semi-hydrogenation.　Considering　the　activity　and　selectivity,　a　four-atom　single-cluster　catalyst　(SCC)　of　Pd1Ti3/TiO2　with　negatively　charged　Pdd-　sites　is　found　to　exhibit　excellent　catalytic　performance.　Moreover,　both　activity　and　selectivity　are　highly　correlated　with　the　surface　properties,　including　the　d-band　center　index　and　surface　work　function.　Our　work　provides　theoretical　guidance　for　the　future　design　of　heterogeneous　SCC　on　reducible　oxide　supports　for　similar　reactions　in　heterogeneous　catalysis.