Abstract: The width-to-length ratios of keyhole edges and the distances among the centers of keyhole edges and that of laser spot were obtained by processing the coaxial images of keyhole,which could indicate the keyhole shape in radial and depth direction.So they were used as keyhole shape parameters to describe the characteristics of keyhole shape.Variations of keyhole shape with welding parameters were studied in this paper.The experimental results indicated that increasing laser power makes keyhole rounder in radcal and much more perpendicular in depth.For lower welding speed,the keyhole shape varies little,and the keyhole will be longer in welding direction and much more inclined in depth for mid-high welding speed.Defocusing distance has few influence on keyhole shape in some range of defocusing distance.