Magnesium,one of the major elements,is important substance for life-sustaining activities. The weathering products of magnesium-containing minerals are transported by river to the ocean,in which magnesium participates in ecosystem material cycling,and finally undergo re-diagenesis as carbonate precipitation. This process is closely related to global carbon cycle. Recently,with the improvement of non-traditional metal isotope systems and the use of MC-ICPMS ( multi-receiver inductively coupled plasma mass spectrometer),the accuracy and convenience of magnesium isotope analysis have been substantially improved. Magnesium plays an important role in the chemical weathering process and life activities and becomes an effective tool for tracing the material sources and various geochemical processes in the surficial environment. Therefore,studying the characteristics and fractionation mechanism of magnesium isotope can help us understand different geochemical processes occurring in the surficial ecosystem and explore the global element cycle and climate changes. This review systematically expounds the magnesium isotopes composition of various components and the controlling factors of fractionation in forest ecosystems. We also summarized the problems existing in the current forest ecosystem research and proposed the future research directions of magnesium isotope in forest ecosystems.