This　study　adopted　femtosecond　laser　with　a　wavelength　of　515　nm　to　drill　high-aspect-ratio　micro　through　holes　on　a　500-μm　thickness　single-crystal　SI-type　4H-SiC　wafer.　Firstly,　through　holes　with　a　high　aspect　ratio　of　20　were　fabricated　in　air.　However,　the　heat　affect　zone　(HAZ),　cracks,　and　surface　material　shedding　around　entrances　and　exits　of　the　holes　are　inevitable　in　air　even　after　chemical　corrosion　post-processing.　In　order　to　remove　these　defects,　the　water-assisted　femtosecond　laser　drilling　of　4H-SiC　was　investigated.　The　high-quality　through　holes　free　of　cracks,　surface　material　shedding,　and　HAZ　were　obtained　under　the　action　of　internal　scour　and　heat　diffusion　of　water.　Besides,　the　water　layer　thickness　and　the　laser　repetition　frequency　have　a　great　influence　on　the　processing　quality　and　efficiency　of　the　micro-holes.　Finally,　high-quality　high-ratio-rate　through　micro-hole　arrays　on　4H-SiC　were　fabricated　with　the　optimal　process　parameters,　which　is　significant　for　the　development　of　SiC　electronic　devices　and　the　high-quality　micro-fabrication　of　other　hard　and　brittle　materials.　©　2020,　Springer-Verlag　London　Ltd.,　part　of　Springer　Nature.