Droplet　collision　is　common　in　nature　and　industrial　processes,　while　understanding　of　the　phenomena　at　high　Weber　numbers　is　not　as　comprehensive　as　the　one　at　low　Weber　numbers.　We　experimentally　investigate　the　collision　dynamics　of　two　droplets　at　high　We　ranging　from　200　to　2000　by　adopting　pure　water　and　pure　ethanol　droplets.　Four　distinct　droplet　collision　regimes　in　the　order　of　increasing　deformation　and　fragmentation　are　reflection　separation,　finger　separation,　stretching　separation　and　splashing.　Due　to　the　larger　inertia　force　and　lower　viscous　force,　water　droplet　collision　is　easier　to　form　finger　separation　and　splashing　regimes　than　ethanol　droplets　under　the　same　We.　The　reinforcement　of　viscous　force　and　surface　tension　weakens　droplet　deformation　and　fragmentation,　and　further　changes　droplet　collision　regime.　Due　to　the　viscous　dissipation　ratio　of　droplet　at　the　maximum　spread　moment　as　a　function　of　Ohnesorge　number　(Oh),　the　model　of　the　maximum　spread　factor　of　coalesced　droplet　is　different　under　various　Oh.　For　a　low　Oh,　a　new　formula　of　the　maximum　spread　factor　is　proposed　by　optimizing　the　maximum　spread　time　in　the　viscous　dissipation　model　based　on　energy　conservation,　which　agrees　well　with　the　experiment.　For　a　high　Oh,　the　formula　of　the　maximum　spread　factor　is　developed　by　using　the　viscous　dissipation　ratio,　and　it　is　consistent　with　the　experiment　as　the　viscous　dissipation　ratio　is　0.8.　©　2022　Elsevier　B.V.