Abstract: There is no general picture to describe the influences of reagent rotational excitation on the reaction, which proceeds via the tunnelling mechanism at collision energies far below the reaction barrier. Here we report a crossed beam study on the prototypical reaction of F+D_2(v=0, j=0, 1)\rightarrowDF(v')+D at collision energies between 44 and 164 cm^-1 with the scheme of multichannel D-atom Rydberg tagging time-of-flight detection. Vibrational state resolved differential cross sections are obtained at v'=2, 3, 4 levels. The effects of reagent rotational excitation were investigated at an equivalent amount of total energy by precise tuning of translational energies. Compared with translation, the rotation of D_2 is found to be more efficient to promote the title reaction. Profound differences introduced by rotation of D_2 are also observed on the angular distribution and quantum state distribution of DF products. We hope the present work could provide an example for understanding the effects of reagent rotational excitation on the chemical reaction at energies that are much lower than the reaction barrier.