Let Λ be a finite-dimensional algebra with finite global dimension, R k = K[X]/(X k ) be the Z-graded local ring with k ≥ 1, and Λ k = Λ ⊗K R k . We consider the singularity category Dsg(mod Z (Λ k )) of the graded modules over Λ k . It is showed that there is a tilting object in Dsg(mod Z (Λ k )) such that its endomorphism algebra is isomorphic to the triangular matrix algebra T k−1 (Λ) with coefficients in Λ and there is a triangulated equivalence between Dsg(mod Z/kZ (Λ)) and the root category of T k−1 (Λ). Finally, a classification of Λ k up to the Cohen-Macaulay representation type is given.Let Λ be a finite-dimensional algebra with finite global dimension, R k = K[X]/(X k ) be the Z-graded local ring with X degree 1 where k is a positive integer, and Λ k = Λ ⊗ K R k . Then Λ k is a positively graded Gorenstein algebra. C. M. Ringel and M. Schmidmeier [49] investigate the Gorenstein projective modules over Λ k with Λ hereditary of type A 2 by using submodule categories, and describe its Auslander-Reiten quiver for k < 6. The structure of this kind of submodule categories has been studied by many people, see [48,49,52,53,54] and the references therein, and have been discovered to be related to weighted projective lines, see [28,29,30] and the references therein.Later, C. M. Ringel and P. Zhang [50] prove that the singularity category of Λ 2 is triangulated equivalent to the triangulated orbit category D b (mod(Λ))/Σ for Λ a path algebra KQ, where Q is an acyclic quiver. X.-H. Luo and P. Zhang generalize these works and introduce monic representations to describe the Gorenstein projective modules over A⊗ K KQ (also A⊗ K (KQ/I) with I generated by monomial relations) with A a finite-dimensional algebra [37,38]. Recently, D. Shen describes Gorenstein projective modules over the tensor product of two algebras in terms of their underlying one-sided modules [51], see also [21].In this paper, we mainly consider the singularity categories D sg (mod(Λ k )) and D sg (mod Z (Λ k )) over Λ k . K. Yamaura [58] proved that for a positively graded self-injective algebra, its stable category of the Z-graded modules admits a tilting object. Following him, we prove that the singularity category D sg (mod Z (Λ k )) of the Z-graded modules over Λ k has a tilting object with the same construction, in particular, its endomorphism algebra is isomorphic to the triangular matrix algebra T k−1 (Λ) with coefficients in Λ. In this way, we get that D sg (mod Z (Λ k )) is triangulated equivalent to the bounded derived category D b (mod(T k−1 (Λ))). Viewing Λ k as a Z/kZ-graded algebra naturally and considering the singularity category D sg (mod Z/kZ (Λ k )), we prove that the above triangulated equivalence induces a triangulated equivalence D sg (mod Z/kZ (Λ k )) ≃ R T k−1 (Λ) . Furthermore, when k = 2, this result recovers the result of [50]: D sg (mod(Λ 2 )) ≃ D b (mod(Λ))/Σ if Λ is hereditary. Finally, we classify Λ k up to the Cohen-Macaulay representation type, and give some examples to describe the Auslander-Reiten quivers for some ...