Genesis of rich iron ore in West Australia is discussed. The authors concider that the Archean-Paleo-Proterozoic Si-Fe formation is typical Sedex and the primary tremendous thick iron-rich sedimentary layer is the main factor for formation of the rich iron ore in West Australia then the ore is further enriched by leaching at surface under special climatic and prolonged stable low hill conditions since Mesozoic Period. Mechanism of leaching enrichment at surface condition is also discussed.