This paper focus on the nature of a high-damping soft elastic material based on Eucommia ulmoides gum (EUG) obtained by epoxidation of EUG first and then in situ reaction between epoxy group and sodium bisulfite. The influence of degree of modification (M mol%) and degree of sulfonation (S mol%) of the product sulfonated E. ulmoides gum (SEUG) on the melting-crystallization behavior, tensile properties and dynamic mechanical properties is analyzed mainly. The results show that M mol% is the key factor in controlling the aggregation structure and static or dynamic mechanical behavior of SEUG, while the introduced sodium bisulfite groups show strengthening and toughening effect to some extent. Besides, the SEUG with high M mol% shows dramatically high tan delta value. With M mol% increasing, the tensile strength and Shore A hardness of SEUG decrease sequentially, while the elongation at break increases visibly. SEUGs with M mol% above 20.3 display soft and elastic stress-strain behavior. At similar M mol% level, SEUG with higher S mol% shows higher tensile strength and lower elongation at break than the one with lower S mol% value. These are attributed to the transformation of the aggregate structure and the introduction of ion interaction. The maximum tan delta value of SEUG reaches up to 2.19. The removal of the restriction effect of crystal region on the molecular motion of amorphous and the increased intermolecular interaction are thought to be main causes.