The　mechanical　properties　degradation　of　cermets　under　high　temperatures　greatly　limits　their　applications.　In　this　paper,　the　compressive　yield　strength　of　WC-Co　based　cermets　at　high　temperatures　was　significantly　improved　by　the　addition　of　Ru.　Based　on　the　detailed　microstructure　analyses,　the　contribution　of　Ru　to　the　plastic　deformation　of　the　cermets　was　disclosed.　The　addition　of　Ru　would　stabilize　the　fcc-Co　structure,　leading　to　an　increase　in　the　proportion　of　the　coherent　WC/Co　phase　boundaries.　The　coherent　phase　boundaries　are　beneficial　to　avoid　stress　concentration　across　the　interface　and　premature　crack　initiation,　inducing　higher　dislocation　densities　and　larger　plastic　deformation　in　both　Co　and　WC　phases.　The　solid　solution　strengthening　effect　of　Ru　and　the　Ru　cluster　in　the　Co　phase　can　inhibit　the　softening　of　the　binder　phase　at　high　temperatures.　The　synergy　of　solid　solution　strengthening　and　dislocation　strengthening　is　responsible　for　the　higher　yield　strength　of　WC-Co　cermets　with　Ru　at　high　temperatures.