Understanding　the　effect　of　acid　strength　on　butene　isomerization　mechanisms　is　essential　in　C4　alkylation　process.　Herein,　the　double　bond,　trans-cis,　and　skeleton　isomerization　mechanisms　of　butene　over　acid　sites　with　different　acid　strengths　were　investigated　utilizing　density　functional　theory　(DFT)　calculations.　It　is　demon-strated　that　the　acid　strength　significantly　affects　the　isomerization　mechanisms　of　butene.　The　stability　of　carbonium　ions　as　reaction　intermediates　follows　the　order:　tert-butyl　cation　＞　cis-butyl　cation　＞　trans-butyl　cation,　which　is　more　sensitive　to　acid　strength　than　that　of　butoxide　species.　Therefore,　the　reaction　pathways　of　double　bond　and　trans-cis　isomerizations　changed　with　varying　the　acid　strength.　Based　on　the　analysis　of　activation　energy　barriers,　it　is　found　that　1-butene　and　2-butene　can　be　easily　converted　into　each　other　over　strong　acid　site.　Thus,　for　reactants,　C4　alkylation　has　no　selectivity　to　1-butene　and　2-butene　over　strong　acid　site,　which　is　consistent　with　experimental　study.　This　work　provides　mechanistic　insights　into　the　relationship　among　acid　strength,　type　of　butene,　and　quality　of　alkylate　in　the　C4　alkylation　process.