  We study the tetraquark state with I^G J^{PC} = 0^+ 1^{-+} in the QCD sum
rule. We exhaust all possible flavor structures by using a diquark-antidiquark
construction and find that the flavor structure 3*6+6*3 is preferred. There are
altogether four independent currents which have the quark contents q s \bar q
\bar s. By using both the Shifman-Vainshtein-Zakharov (SVZ) sum rule and the
finite energy sum rule, these currents lead to mass estimates around 1.8 - 2.1
GeV, where the uncertainty is due to the mixing of two single currents. Its
possible decay modes are S-wave b_1(1235) \eta and b_1(1235) \eta^\prime, and
P-wave KK, \eta \eta, \eta \eta^\prime and \eta^\prime \eta^\prime, etc. The
decay width is around 150 MeV through a rough estimation.
