Abstract: High strength galvanized steel plates (HC450/780DPD+Z) are commonly used in automobile industry, the research about laser overlap welding is carried out by using fiber laser, the influence of overlap gap on the microstructure and mechanical properties of laser welded joint was analyzed, and then microstructure and microhardness of welded joint were observed and tested at a constant overlap gap. The results show that the shape of seam melting changes obviously with the increase of overlap gap, the shape changes gradually from “waist” to “barrel” type, and the phenomenon of tensile-shear stress increases first and then decreases.