Laser-arc　hybrid　welding　is　one　of　the　advanced　joining　techniques.　By　using　instruments　such　as　a　high-speed　camera　and　a　laser　power　meter,　the　effects　of　a　vertically　incident　CO2　laser　beam　on　characteristics　of　a　DC　tungsten　inter-gas　arc　are　investigated.　Results　demonstrate　that　the　laser-arc　interaction　causes　the　curve　of　arc　static　characteristic　to　shift　downwards,　the　arc　column　to　expand,　the　electric　power　to　decease　and　the　total　arc　power　increase.　With　the　increase　of　the　laser　power,　the　downward　shift　of　the　static　characteristic　curve　increases,　but　the　total　arc　power　increases.　The　lower　the　arc　current　is　and　the　nearer　the　laser　beam　locates　to　the　cathode,　the　more　the　arc　voltage　decreases,　which　the　expansion　of　the　arc　column　mainly　occurs　in　the　range　between　the　laser　beam　location　and　the　anode.