The　fracture　failure　mechanism　of　high-temperature　structural　materials　plays　a　vital　role　in　the　application　of　high-temperature　structural　materials.　Transmission　electron　microscopy　(TEM)　is　a　unique　tool　providing　the　internal　microstructures　and　defects　of　images　in　samples　with　up　to　atomic　resolution.　However,　great　challenges　are　posed　to　the　realization　of　atomic-scale　observation　under　thermal-mechanical　coupling　conditions　in　TEM.　In　this　work,　a　thermomechanical　testing　apparatus　combining　micro-electro-mechanical　system　(MEMS)　technology　with　a　miniature　piezoelectric　ceramic　inside　TEM　was　developed,　which　enabled　in-situ　mechanical　testing　and　high-resolution　TEM　analysis　at　elevated　temperatures　up　to　873　K.　This　unique　technique　was　used　to　investigate　the　atomic-scale　fracture　mechanism　of　nickel-based　superalloy　DD6　at　high　temperatures　and　stress　for　the　first　time.　The　fracture　mode　where　cracks　propagate　along　the　γ　and　γ′　phase　interfaces　was　proposed.　Furthermore,　the　role　of　60°　full　dislocations　at　the　crack　tip　in　crack　propagation　was　revealed.　©　2024　The　Authors