In this paper we construct bases of standard modules L(Lambda) for affine Lie
algebra of type B_2^(1) consisting of semi-infinite monomials. The main
technical ingredient is a construction of monomial bases for
Feigin-Stoyanovsky's subspaces W(Lambda) of L(Lambda) by using simple currents
and intertwining operators in vertex operator algebra theory. By coincidence
W(k Lambda_0) for B_2^(1) and the standard module L(k Lambda_0) for A_1^(1)
have the same presentation P/I, so our main theorem provides a new proof of
linear independence of monomial bases of A_1^(1)-modules L(k Lambda_0).