Glycine tomentella Hayata is a species of Glycine Willd. subgenus Glycine, and in China it is distributed along the southeast coast. In this study, 11 natural G. tomentella populations were collected and their genetic diversity levels and population structures were analyzed using 25 simple sequence repeat (SSR) markers. The number of alleles per locus averaged 7.16 and ranged from 2 to 17. The expected heterozygosity (He) per locus averaged 0.60, varying from 0.19 to 0.86. The G. tomentella populations on these Chinese islands showed a greater average genetic variation (60.96%) among populations and gene differentiation index (Gst= 0.607), and a lower average within-population genetic variation (33.47%) and gene flow (Nm= 0.162). In this study, these G. tomentella island populations were characterized by a relatively greater average multilocus outcrossing rate of 5.74%, which may the result of heterogeneity owing to the perennation of G. tomentella. A spatial autocorrelation analysis revealed that populations within a radius of approximately 30.45 km had positive and significant genetic relationships. The Neighbor-Joining (NJ) and STRUCTURE analyses strongly showed a pattern of ‘island differentiation’ for the populations on southeast islands of China and also suggested that some genetic interconnection occurred along the southeast coast of China. The F-statistics suggested that geographically different G. tomentella populations had specific population structures. We propose that when collecting this species as a genetic resource, every G. tomentella population should be sampled.