The　controllable　preparation　of　silver　nanowires　(AgNWs)　with　a　high　aspect　ratio　is　key　for　enabling　their　applications　on　a　large　scale.　Herein,　the　aspect　ratio　regulation　of　AgNWs　mediated　by　halogen　ion　composition　in　ethylene　glycol　system　was　systematically　investigated　and　the　size　evolution　mechanism　is　elaborately　understood.　The　co-addition　of　Br−　and　Cl−　results　in　AgNWs　with　the　highest　aspect　ratio　of　1031.　The　surface　physicochemical　analysis　of　AgNWs　and　the　density　functional　theory　calculations　indicate　that　the　co-addition　of　Br−　and　Cl−　contributes　to　the　much-enhanced　preferential　growth　of　the　Ag(111)　crystal　plane.　At　the　same　time,　when　Cl−　and　Br−　coexist　in　the　solution,　the　growth　of　the　Ag(100)　crystal　plane　on　the　AgNWs　was　restrained　compared　with　that　in　the　single　Cl−　system.　Resultantly,　the　enhanced　growth　of　Ag(111)　and　the　inhibited　growth　of　Ag(100)　contribute　to　the　formation　of　AgNWs　with　a　higher　aspect　ratio　in　the　Cl–Br　mixed　solution.　The　results　can　provide　new　insights　for　understanding　the　morphology　and　size　evolution　during　the　AgNWs　preparation　in　ethylene　glycol　system.　©　2022　by　the　authors.