Thermoelastic　damping　(TED)　is　one　of　the　main　energy　dissipation　sources　of　high　performance　resonators　at　room　temperature,　however,　the　classical　TED　model　fails　at　the　nano-scale　due　to　the　influence　of　small　scale　effect.　In　this　paper,　a　novel　TED　model　is　proposed　to　estimate　the　impact　of　both　mechanical　and　thermal　small　scale　effects　on　TED　of　nano-resonators.　The　surface　elastic　theory　and　the　dual-phase-lag　heat　conduction　model　(DPL　model)　are　first　combined　to　establish　the　TED　model.　Analytical　expression　of　the　TED　model　is　derived,　which　can　reduce　to　the　classical　TED　model.　In　numerical　simulations,　a　critical　thickness　is　proposed　to　identify　the　influence　of　small　scale　effect　on　TED.　Small　scale　effect　significantly　improves　TED　of　resonators　within　the　critical　thickness,　which　however　can　be　neglected　as　the　resonator　thickness　is　greater　than　the　critical　thickness.　Moreover,　surface　effect　has　stronger　effect　than　non-Fourier　heat　conduction　on　improving　TED　of　nano-resonators.　Additionally,　influences　of　the　other　key　factors　on　TED　are　examined　in　detail.　This　paper　provides　a　more　reasonable　theoretical　approach　to　estimate　TED　in　the　design　of　high　performance　nano-resonators.　©　2021