The　splat　is　the　fundamental　unit　of　thermally　sprayed　coatings,　which　has　been　one　of　the　hottest　issues　for　decades.　In　order　to　study　the　splat　formation,　an　experiment　was　designed　and　conducted,　in　which　a　millimeter-size　nickel　metal　droplet　fell　freely　and　impacted　on　aluminum　and　stainless　steel　substrate.　The　microstructural　characteristics　of　the　splat　and　the　heat　conduction　and　solidification　processes　during　the　flattening　process　have　been　studied　numerically　and　experimentally.　The　effect　of　the　droplet　temperature,　impact　velocity　as　well　as　the　substrate　temperature　was　investigated.　The　phenomenon　of　substrate　melting　was　observed　after　the　spreading　of　nickel　droplet,　which　became　more　pronounced　when　the　initial　substrate　temperature　increased.　Increasing　the　impact　velocity　of　droplet　resulted　in　a　decrease　in　the　interfacial　temperature　between　droplet　and　substrate.