  We re-examine the level-one irreducible highest weight representations of the
quantum affine superalgebra $U_q(\hat{sl}(2|1))$ and derive the characters and
supercharacters associated with these representations. We calculate the
exchange relations of the vertex operators and find that these vertex operators
satisfy the graded Faddeev-Zamolodchikov algebra. We give an integral
expression of the correlation functions of the q-deformed supersymmetric t-J
model and derive the difference equations which they satisfy.
