  In this article we have calculated the spin-independent cross section of
nucleon-dark matter scattering process at loop level, which is relevant to dark
matter direct detection. Paying particular attention to the scattering of gluon
with dark matter, which contributes as leading order in the perturbation, we
have systematically evaluated loop diagrams with tracking the characteristic
loop momentum which dominates in the loops. Here loop diagrams whose typical
loop momentum scales are the masses of quarks and other heavier particles are
separately presented. Then, we have properly taken into account each
contribution to give the cross section. We assume that the dark matter is pure
bino or wino in the supersymmetric models. The application to other models is
straightforward.
