Unravelling　the　influence　of　strain　and　geometric　effects　on　the　electrochemical　reduction　of　carbon　dioxide　(CO2RR)　on　Cu-based　(or　Pd-based)　alloys　remains　challenging　due　to　complex　local　microenvironment　variables.　Herein,　we　employ　two　PdCu　alloys　(nanoparticles　and　nanodendrites)　to　demonstrate　how　CO2RR　selectivity　can　shift　from　CO　to　HCOO−.　Despite　sharing　consistent　phases,　exposed　crystal　facets,　and　overall　oxidative　states,　these　alloys　exhibit　different　local　strain　profiles　due　to　their　distinct　geometries.　By　integrating　experimental　data,　in-situ　spectroscopy,　and　density　functional　theory　calculations,　we　revealed　that　CO2　prefers　adsorption　on　tensile-strained　areas　with　carbon-side　geometry,　following　a　*COOH-to-CO　pathway.　Conversely,　on　some　compressive-strained　regions　induced　by　the　dendrite-like　morphology,　CO2　adopts　an　oxygen-side　geometry,　favoring　an　*OCHO-to-HCOO　pathway　due　to　the　downshift　of　the　d-band　center.　Notably,　our　findings　elucidate　a　dominant　*OCHO-to-HCOO−　pathway　in　catalysts　when　featuring　both　adsorption　geometries.　This　research　provides　a　comprehensive　model　for　local　environment　of　bimetallic　alloys,　and　establishes　a　clear　relationship　between　the　CO2RR　pathway　shift　and　variation　in　local　strain　environments　of　PdCu　alloys.　©　The　Author(s)　2024.　Published　by　Oxford　University　Press　on　behalf　of　China　Science　Publishing　&　Media　Ltd.