With the development of iron isotope measuring techniques in marine environmental media，especially the isotopic composition of different forms of iron in seawater and sediments，iron isotopes have demonstrated a new tracer role for various biogeochemical processes. Based on the framework of the proprietary fractionation mechanism between different iron valences and forms of occurrence，this paper summarizes the range of iron isotopes in different sources，comprising atmospheric deposition，landsource runoff，sediments，groundwater，and submarine hydrothermal fluids in the modern marine environment. The biogeochemical processes of the internal iron cycle in the ocean are discussed，including iron isotope fractionation mechanism for biological uptake，transformation of particulate/dissolved iron，and scavenging. The dominant controlling factors for the iron isotope composition of seawater profiles at different horizons are discriminated. In addition，the application of the traceable endmember mixing model to identify iron sources in the Atlantic Ocean，the Pacific Ocean，and the Southern Ocean has verified the close relationship between global climate change and the sea/land multiple physical and chemical processes; special iron isotope data of distinct iron mineral with different crystallinity and reaction activity could be used to trace the depth and extent of iron reduction in early diagenesis，which can also help to distinguish iron isotope data from ancient marine sediments and improve the reconstruction accuracy of paleoredox environments.