Abstract: Described are a self-healing composition, and a preparation method for and an application of the composition. The composition is of a core-shell structure; the core contains a hydrogenated styrenic thermoplastic elastomer polymer and an inorganic filler; the shell contains a hydrophilic polymer; the composition has a density of 1.2-2 g/cm3, a water contact angle of no more than 90°, and a diesel oil and/or natural gas absorption expansion ratio of 5-15 times. By coating the hydrogenated styrenic thermoplastic elastomer and the inorganic filler with the hydrophilic (surface polarized) polymer, a core-shell structure is formed. When the composition is used for well cementing in an oil/gas field, the composition has a density and compatibility matching cement mortar and thus can form a uniform and stable cement slurry for well cementing in the oil/gas field, and has excellent oil/gas absorption expansion performance and thus can expand after absorbing oil/gas to perform self-healing.