  The inclusive hadronic production of $\eta_Q$($\eta_c$ or $\eta_b$) pair is
proposed to extract the transverse momentum dependent(TMD) gluon distribution
functions. We use nonrelativistic QCD(NRQCD) for the production of $\eta_Q$.
Under nonrelativistic limit TMD factorization for this process is assumed to
make a lowest order calculation. For unpolarized initial hadrons, unpolarized
and linearly polarized gluon distributions can be extracted by studying
different angular distributions.
