Spin polarization at benzene/Ni organic/ferromagnetic interface is investigated by applying different substituting side groups. Based on first-principle calculations, it is demonstrated that the spin polarization of the states may be tuned in magnitude and sign by the side groups, which depends on the type of side groups as well as their position in the aromatic ring. Especially, a spatial spin polarization modulation is realized at the surface with the utilization of electron donating group -NH2 or electron accepting group -NO2. The analysis of projected density of states onto the p(z) orbital of carbon atoms indicates that the side group reduces the structural symmetry of the molecule and changes the p(z) orbital of carbon atom at different position, which further modifies the p(z)-d orbital hybridization as well as the spin transfer between the molecule and the ferromagnet. This work indicates a feasible way to modulate the spatial spin polarization at organic spinterface by side groups, which deserves to be measured by spin-polarized scanning tunneling microscopy. (C) 2017 Elsevier B.V. All rights reserved.