Let R∈Mn(Z) be an expanding matrix and D={0,a1,a2,⋯,aN−1}u≡{0,1,⋯,N−1}u (modN) be a N-element digit set, where u∈Zn∖{0}. In this paper, we study the spectral property of the self-affine measures μR,D which is generated by D and R, and obtain a sufficient condition such that μR,D is a spectral measure. Moreover, for a special case, we give a necessary and sufficient condition such that μR,D is a spectral measure, and the exact spectrum of μR,D is given.