The　characteristics　of　both　laser　beam　and　TIG　arc　are　investigated　during　the　interaction　between　the　vertical　incident　laser　and　TIG　arc　by　using　a　laser　power　meter,　a　beam　quality　diagnosis　instrument　and　a　high　speed　camera.　The　experimental　results　demonstrate　that,　when　CO2　laser　beam　passes　through　TIG　arc,　the　laser　power　is　attenuated　dramatically,　the　beam　is　defocuses　and　even　a　laser　supported　combustion　wave　is　generated.　In　this　case,　the　beam　quality　is　seriously　worsened.　On　the　other　hand,　the　arc　voltage　is　dropped　and　the　arc　column　is　expanded.　However,　the　beam　power,　beam　diameter,　arc　voltage　and　arc　column　seldom　change　during　TIG　arc　interacted　with　Yb:YAG　laser.　Under　the　experimental　conditions,　the　inverse　bremsstrahlung　absorption　coefficient　calculated　is　14.14-26.29　m-1　for　CO2　laser,　1.1-2.03　m-1　for　YAG　laser　and　the　refractive　index　is　0.99249-0.99454　for　CO2　laser,　0.99992-0.99994　for　YAG　laser,　respectively.　The　inverse　bremsstrahlung　absorption　coefficient　for　YAG　laser　is　two　orders　of　magnitude　lower　than　that　for　CO2　laser.　Meanwhile,　there　is　less　difference　between　the　refractive　index　of　YAG　laser-TIG　and　YAG　laser-air,　so　there　is　no　obvious　refraction　of　the　TIG　arc　to　the　YAG　laser,　which　is　the　main　reason　for　the　great　difference　between　the　CO2　laser-TIG　and　YAG　laser-TIG　interaction.