Agricultural　drought　differs　from　meteorological,　hydrological,　and　socioeconomic　drought,　being　closely　related　to　soil　water　availability　in　the　root　zone,　specifically　for　crop　and　crop　growth　stage.　In　previous　studies,　several　soil　moisture　indices　(e.g.,　the　soil　moisture　index,　soil　water　deficit　index)　based　on　soil　water　availability　have　been　developed　for　agricultural　drought　monitoring.　However,　when　developing　these　indices,　it　was　generally　assumed　that　soil　water　availability　to　crops　was　equal　throughout　the　root　zone,　and　the　effects　of　root　distribution　and　crop　growth　stage　on　soil　water　uptake　were　ignored.　This　article　aims　to　incorporate　root　distribution　into　a　soil　moisture-based　index　and　to　evaluate　the　performance　of　the　improved　soil　moisture　index　for　agricultural　drought　monitoring.　The　Huang-Huai-Hai　Plain　of　China　was　used　as　the　study　area.　Overall,　soil　moisture　indices　were　significantly　correlated　with　the　crop　moisture　index　(CMI),　and　the　improved　root-weighted　soil　moisture　index　(RSMI)　was　more　closely　related　to　the　CMI　than　averaged　soil　moisture　indices.　The　RSMI　correctly　identified　most　of　the　observed　drought　events　and　performed　well　in　the　detection　of　drought　levels.　Furthermore,　the　RSMI　had　a　better　performance　than　averaged　soil　moisture　indices　when　compared　to　crop　yield.　In　conclusion,　soil　moisture　indices　could　improve　agricultural　drought　monitoring　by　incorporating　root　distribution.　©　2017　American　Water　Resources　Association