Using a Generic spin basis, we present a general formalism of one-loop radiative corrections to the spin correlations in the top quark pair production at the Next Linear Collider, and calculate the O(α_s) QCD corrections under the soft gluon approximation. We find that: (a) in Off-diagonal basis, the O(α_s) QCD corrections to e_L^- e^+ (e_R^- e^+) scattering process increase the differential cross sections of the dominant spin component t_↑t̅_↓ (t_↓t̅_↑) by ∼ 30 √(s)=400 GeV and 1 TeV,

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... ely; (b) in Off-diagonal basis (Helicity basis), the dominant spin component makes up 99.8 the total cross section at both tree and one-loop level for √(s)=400 GeV, and the Off-diagonal basis therefore remains to be the optimal spin basis after the inclusion of O(α_s) QCD corrections.