For　the　fuel　economy　of　a　series-parallel　plug-in　hybrid　electric　vehicle　(PHEV)　as　the　research　target,　in　order　to　improve　the　control　effect　of　the　instantaneous　equivalent　fuel　consumption　minimization　strategy　(ECMS),　allowed　for　the　relationship　of　the　battery　state　of　charge　(SOC),　equivalent　factor　and　equivalent　fuel　consumption,　the　global　optimization　model　of　the　equivalent　factor　is　built.　The　equivalent　factor　S　is　offline　optimized　by　genetic　algorithm　(GA)　to　obtain　the　MAP　of　the　optimization　equivalent　factor　between　the　different　ranges　and　the　battery　SOC　value.　The　energy　management　strategy　based　on　the　optimization　equivalent　factor　of　ECMS　is　proposed.　And　considering　the　efficiency　of　the　battery　motor　and　other　components,　the　power　distribution　of　the　engine,　ISG　and　drive　motor　is　gained　based　on　the　best　equivalent　factor　of　ECMS.　Conducted　with　hardware　in　the　loop　simulation　experiment,　the　simulation　results　show　that　compared　with　the　equivalent　factor　which　is　not　optimized,　the　vehicle　fuel　economy　increases　by　20.82%.　And　the　results　between　hardware　in　loop　experiment　and　simulation　are　basically　identical.　It＇s　indicated　the　feasibility　and　effectiveness　of　the　proposed　energy　management　strategy.　Also　it　provides　theoretical　basis　on　solving　the　power　allocation　strategy　of　the　different　ranges　of　PHEV.　©　2016　Journal　of　Mechanical　Engineering.