Abstract: The high power density of laser makes laser welding process become one of the most promising and efficient welding method.The high power laser welding with filler wire of 10 mm and 12 mm thick plates was studied, and the plasma behavior was analyzed as well.The results showed when the laser power is over 13 kW, the penetration curve becomes gentler and the gradient declines obviously.However, in regard to the fully-penetrated seam, it could not fully demonstrate the effects of the welding parameters on the cross-section only with width and penetrations of the weld bead.The cross-section of fully-penetrated bead appears to be a Y shape.And this kind of Y shape is further designed to be a combination with an inverted trapezoid on the top and a rectangle below.In this way, wire feeding rate and gap are varied in order to study their effects on the Y shape bead dimensions while laser power and welding speed keeping constant.In addition, the influence of plasma of the protective gas was studied.