Characterizing　immiscible　metallic　composites　with　electron　microscopy　and　X-ray　spectroscopy　is　the　classic　way　of　obtaining　their　structural　and　physical　details.　Nevertheless,　such　a　combination　lacks　ability　to　tell　the　interfacial　interactions　at　grain　boundaries.　Here　we　demonstrate　a　novel　strategy　to　uncover　the　mystery　of　interfacial　interactions　in　such　systems　by　spectroscopic　microscopy.　The　morphological　and　spectral　data　of　samples　were　simultaneously　recorded　and　analyzed,　which　reveals　critical　information　regarding　interfacial　electronic　modes.　Taking　W-Cu　as　a　model,　we　experimentally　quantified　its　connectivity　and　unambiguously　identified　conditional　bonding　between　W　and　Cu.　Further,　we　chemically　reconstructed　the　specific　W-Cu　boundary　that　possessed　the　strongest　interactions　and　investigated　its　atomic　structure.　The　mechanism　of　W-Cu　bonding　was　proposed　and　verified　by　first-principle　calculations.　The　above　methodology　holds　great　promise　to　serve　as　a　universal　approach　in　achieving　in-depth　understanding　of　immiscible　composites.　??　2022　Published　by　Elsevier　Ltd　on　behalf　of　The　editorial　office　of　Journal　of　Materials　Science　&　Technology.