In this paper we analyze and discuss the characteristics of internal friction of metallic glasses near glass transition temperature Tg based on the model of free volume and mechanical theory of solids. The relationship between stress and strain was obtained if the proportion occupied by solid-like and liquid-like regions in the matrix of glassy state was considered. It is found theoretically that the internal friction peak being of relaxation type can appear in the vicinity of Tg and the modulus decrease dramatically during glass transition. The theoretical analysis is essentially in agreement with experimental results.