Abstract: The influence of coaxial shielding gas flux on keyhole was studied by processing the captured coaxial image of keyhole.The results show that the coaxial shielding gas has great influence on the upside of keyhole and its influence on keyhole bottom is weak.For more flux of coaxial shielding gas,the radial dimension of outer edge of keyhole increases but the radial dimension of inner edge of keyhole varies little.The distances from the centers of keyhole edges to that of laser spot decrease with increasing the flux of coaxial shielding gas,which indicates that the vertical axis of keyhole is nearer to that of laser beam.In general,coaxial shielding gas has little influence on keyhole.