Due　to　the　low　strength　and　poor　durability　of　plain　soil,　and　the　roughly⁃　estimated　proportion　of　modified　materials　determined　from　craftsman’　s　experience,　the　surface　of　rammed　earth　(RE)　is　always　susceptible　to　cracking　and　spalling.　Hence,　the　mix　proportion　of　modified　RE　(MRE)　shall　be　designed　based　on　the　parameters　of　actual　soil　and　reasonable　testing　method.　Most　existing　studies　are　limited　to　obtaining　a　single　performance　index⁃based　optimum　mix　proportion　of　MRE.　However,　the　mix　proportion　of　actual　MRE　shall　be　optimized　by　synchronously　considering　multiple　mechanical　and　durability　indexes,　and　meanwhile　the　relative　importance　of　variables　in　different　regions　and　climatic　conditions　shall　be　evaluated.　Furthermore,　in　the　existing　researches,　only　the　optimum　group　is　determined　from　several　predefined　mix　proportions,　which　is　different　from　the　optimum　mix　proportion　within　the　preset　content　range　of　the　modified　material.　In　this　work,　a　design　method　of　determining　the　optimum　mix　proportion　of　MRE　is　proposed　by　combining　the　mechanical　and　durability　performance　indexes.　The　design　method　includes　1)　selection　principles　of　earth　material　and　identification　method　of　soil　properties;　2)　a　multi⁃indexes⁃based　comprehensive　weighting　method　of　MRE;　3)　comparison　and　optimization　of　the　mix　proportion　of　modified　MRE　based　on　weighted　score　and　regression　analysis.　The　proposed　method　screens　out　the　appropriate　mix　proportion　of　MRE　by　adjusting　the　index　weight　according　to　the　varying　importance　of　indexes.　Through　the　optimized　design,　the　optimum　mix　proportion　of　each　modified　material　within　the　preset　content　range　can　be　acquired.　Based　on　the　designed　example,　it　is　validated　that　the　optimum　mix　proportion　of　MRE　can　indeed　be　determined　by　the　proposed　method.　©　2024　Chinese　Society　of　Civil　Engineering.　All　rights　reserved.