The　numerical　manifold　method　(NMM)　is　superior　in　discontinuous　analysis,　benefiting　from　its　bi-cover　systems,　i.e.,　the　mathematical　cover　and　the　physical　cover.　In　this　work,　the　NMM　is　devoted　to　compute　the　T-stress　for　two-dimensional　functionally　graded　materials　(FGMs)　with　multiple　cracks.　The　displacement　field　for　cracked　FGMs　is　firstly　solved　by　the　NMM　and　then　the　related　T-stress　is　evaluated　in　the　NMM　postprocessing　via　the　interaction　integral　method.　Two　typical　examples　are　firstly　tested　to　verify　the　accuracy　of　the　proposed　method　and　the　domain-independence　of　the　interaction　integral,　and　then　another　three　cases　are　examined　to　reveal　the　effects　of　material　gradients,　crack　geometries　and　boundary　conditions　on　the　T-stress.