Chain conformational distribution in a two dimensional space of the chain dimension and the conformational energy have been studied using the rotational isomeric state model in the present work.It shows that (1) the number of chain conformation considerably enhances in the area of small chain dimensions; (2) in the small chain dimension area there still exist some of stable chain conformations; (3) these conformations in the small chain dimension area possess structures of rod like shape; (4) the chain conformational distribution studied implies an asymmetry of entropy elasticity of the polymer chain system.