Cu film deposited on ZrN and TaN diffusion barriers is annealed in vacuum and H2, N2 mixed gas respectively. SEM morphology, XRD and resistivity are employed to characterize the thermal stability of the multilayer. The experiment demonstrates that for the multilayer deposited on the same kind of diffusion barrier, the thermal stability of multilayer annealed in H2, N2 mixed gas is superior to that annealed in vacuum. While for the multilayer annealed in vacuum, the thermal stability of the multilayer deposited on ZrN diffusion barrier is better than that deposited on TaN diffusion barrier. The investigation shows that the evaluation of the thermal stability of the multilayer should take not only some intrinsic factors of the multilayer itself, for instance diffusion barriers, but also the annealing ambient into account.