An　improved　grey　wolf　optimization　(IGWO)　algorithm　is　presented　to　determine　the　optimal　combination　of　a　WT-PV-BS-DE　islanded　microgrid　in　order　to　achieve　a　cost　effective　and　reliable　hybrid　generation　system.　As　the　traditional　grey　wolf　optimization　(GWO)　algorithm　has　the　disadvantages　of　slow　convergence　and　high　possibility　of　being　trapped　in　local　optimum,　the　proposed　IGWO　algorithm　used　Tent　chaos　mapping　strategy　to　generate　the　initial　population,　which　increases　the　diversity　of　the　population.　Then,　the　convergence　factor　is　dynamically　adjusted　to　maintain　a　better　balance　between　global　search　and　local　search.　Thirdly,　Cauchy　mutation　operator　is　carried　out　on　the　current　optimal　individual　of　each　generation,　thus　it　could　effectively　jump　out　of　local　minima.　Finally,　the　IGWO　is　applied　for　optimal　sizing　of　wind　power-photovoltaic　modules　cells-battery　storage-diesel　generation　islanded　microgrid,　in　which　the　optimization　objective　is　minimizing　of　annualized　system　cost　and　the　constraint　condition　are　power　supply　reliability.　The　results　show　the　effectiveness　and　applicability　of　the　proposed　method.　©　2022,　Solar　Energy　Periodical　Office　Co.,　Ltd.　All　right　reserved.