A model of Σ5〈001〉/(210) high angle grain boundary (GB) in austenite phase in steel was set up with computer programming. The environment-sensitive embedding energies (ESE) of C, N and microalloying elements in grains or in GB core are c alculated by recursion method, respectively. The segregation and interaction of C, N and microalloying elements in the GB core were discussed. Calculation resul ts show that: discrete light impurities C and N tend to segregate in the GB area , forming atomic clusters; microalloying elements are liable to distribute in pe rfect austenite grains. Ti, V, Nb occupy the top sites of the trigonal prism for med by iron in the GB core, and Ti, V, Nb can also form atomic clusters in GB co re like C or N. When the temperature is decreased and the concentration of C, N and microalloying elements reach to the limit of solubility, the C, N compounds of microalloying elements precipitate from the matrix in GB core of austenite in steel. These compounds can act as heterogeneous nuclei of austenite phase in th e course of recrystallization and retard the growth of austenite grains, leading to the refinement of austenite grains. Nb is the most efficient refiner of micr oalloying elements Nb, Ti, V.