Cd contamination of soils has aroused great concerns among the people the world over for its causing Cd concentration in food crops beyond the limit for food safety, thus posing a threat to human health via the food chain. Migration and transformation of cadmium in soil, uptake of cadmium by plant roots, transport and storage of cadmium in different organs of plants are critical processes of the biogeochemical cycling of cadmium in the soil-plant systems. In recent years, the technique of stable isotope fractionation has been applied to investigation of cadmium transfer and storage in soil-plant systems, providing new insights into the transformation of cadmium in different soil pools and plant compartments. In this study, a brief introduction is presented first to the fundamental principle and methodology of cadmium isotopic composition analysis. And then discussions in detail are made about directions and extents of the Cadmium isotopes fractionation in soil induced by a number of processes, such as dissolution of soil minerals, precipitation, adsorption, and chelation with organic matter, with special emphasis laid on mechanisms of the fractionation of Cd in different plant parts during the three critical processes, that is, cadmium uptake by plant roots, cadmium translocation from root to shoot and cadmium storage in grains. To the best of our acknowledge, fractionation of cadmium isotopes in soil-plant systems may be subject to impacts of a number of factors/processes, such as soil minerals, composition of organic matter, root exudates and microorganisms in the rhizosphere, type of plants, stage of plant growth, nutrient elements with antagonistic effect, and so on. However, it remains as of yet unclear as to how. In the end, based on the status quo of the research on cadmium isotopes fractionation in soil-plant systems, perspectives for future research are put forth to encourage a combined application with other techniques, such as spectroscopy-based speciation analyses, molecular biological analyses, and so on, in the hope that the future research may provide a better understanding of the mechanisms of cadmium transformation in soil-plant systems, and help develop regulation strategies and remediation technologies for safe production of crops in cadmium-contaminated soils.