The burnout of zinc is one of the key problems in laser welding of galvanized steel. In this paper, the burnout width of the zinc layer on both the top and the bottom of the weld and the zinc content in the middle layer of the weld zone were measured, and the weight gain ratio after the corrosion tests was obtained. The relationships between process parameters and the spectral signals of the laser-induced plasma as well as the burnout of the zinc were experimentally studied in laser lap welding of galvanized steel. The results have shown that: 1) the important order of the relevant factors affecting the burnout of the zinc is welding speed>laser power>auxiliary gas flow> defocus; 2) the burnout rate of the zinc is increased with the increase of the intensity of zinc line Zn I 328.2 nm and Zn I 330.3 nm; and 3) pores are generated because of the evaporation of the zinc. The more zinc content exists around the pore wall, the larger the diameter of the pore is. The intensity of the zinc line can be used for the on-line monitoring of the dynamic rate of the zinc burnout and the pore produced in the laser welding process.