An exemplary damascene interconnect structure includes a substrate (20), a first dielectric layer (21) on the substrate, a plurality of trenches (27) formed in the first dielectric layer, and a plurality of metal lines (24) filled in the trenches. The first dielectric layer includes multi sub-dielectric layers (211, 212, 213). Wherein a plurality of air gaps (28) are maintained between the metal lines and at least one of the sub-dielectric layers. A method for fabricating the damascene interconnect structure is also provided.