This　paper　looks　into　the　current　status　of　jet　engines　and　try　to　point　a　direction　for　its　future　development.　First　we　study　the　jet　engines　by　looking　at　past　development　in　their　structure.　Jet　engines　used　in　civil　and　military　environment　have　different　development　directions.　By　using　the　results　and　statistics,　we　can　determine　in　which　way　their　structure　can　be　improved.　Also,　one　of　the　potential　pathways　is　to　switch　to　using　bio-jet　fuel,　one　of　the　most　matured　alternative　fuel.　Bio-jet　fuel　can　lower　jet　engine＇s　overall　greenhouse　gas　emission　and　slightly　improve　its　efficiency　according　to　studies　this　paper　investigated.　This　paper　studies　the　effect　of　bio-jet　fuel　on　jet　engines　and　then　evaluates　the　various　bio-jet　fuel　options.　Another　pathway　is　by　adopting　hydrogen　technology,　which　has　the　potential　of　eliminating　all　direct　greenhouse　gas　emission,　but　the　technology　is　still　under　development.　This　paper　looks　into　natural　gas-hydrogen　hybrid　engines,　which　is　one　of　the　most　promising　options.　Finally　this　paper　try　to　create　a　roadmap　for　future　jet　engine　development,　finding　out　solutions　to　the　problems　of　previously　discussed　technologies.　©　2021　IEEE.