Based on many experiments of CO2 laser welding of 1.5 mm zinc coated high strength steel to vehicle body, joint microstructure and stress-strain curve of specimen are acquired. Given special welding technology, theoretical Pc-v curve and Pc-Δf curve of stable deep penetration laser welding are deduced. The unstable sharply gasification of zinc enlarges heat-affected zone (HAZ), debases welding stability and increases the difficulty of protecting condenser. Through optimizing technology parameter, adopting coaxial and side blown protective gas, deep penetration laser welding can effectively avoid softening HAZ of welding of zinc coated high strength steel and can control the gas hole. The experimental result indicates that the content welding quality can be gained on the condition of using N2 as protective gas ,the laser power at 1300 W, the welding speed at 0.8～1.1 m/min and defocusing amount at Δf=-0.4 mm, the hardness of welding seam is twice as that of base material.