Designing　high-performance　catalyst　is　vital　in　the　field　of　CO2　methanolization.　In　this　study,　two　In3Ru　surfaces　(In3Ru_i　and　In3Ru_r)　were　employed　as　computational　models　and　the　density　functional　theory　was　applied　to　study　the　influence　of　surface　In/Ru　ratio　on　their　surface　morphologies,　reaction　mechanisms　and　catalysis　performance　for　methanol　synthesis.　Surface　characterization　reveals　that　In3Ru_i　is　higher　in　surface　In/Ru　ratio　than　In3Ru_r,　and　such　difference　facilitates　CO2　adsorption　on　In3Ru_r.　Being　different　in　surface　In/Ru　ratio,　two　surfaces　exhibit　distinct　variations　in　the　reaction　mechanism　of　methanol　formation.　For　In3Ru_i,　the　＂Formate＂　pathway　dominates　the　first　CO2　activation　step　which　leads　to　methanol　production.　On　the　other　hand,　In3Ru_r　prefers　the　＂reverse　water-gas　shift＂　pathway　(RWGS)　in　the　initial　step　of　CO2　activation,　but　this　mechanism　is　unable　to　generate　CH3OH　due　to　the　kinetic　limitation　of　CO*　hydrogenation.　Based　on　the　microkinetic　modeling,　In3Ru_i　is　superior　in　both　CO2　production　rate　and　CH3OH　selectivity　than　the　other　one,　suggesting　higher　surface　In/Ru　ratio　benefits　methanol　formation,　which　complies　well　with　the　experiment.　Overall,　our　study　offers　a　new　perspective　with　respect　to　how　surface　morphology　of　the　bimetallic　catalyst　influences　the　reaction　mechanisms　of　CO2　hydrogenation.