It has been carried out the test and research to the stainless steel plate laser welding welded seam, by two-dimensional, three-dimensional appearance observation and tensile methods. Its result is: The YAG laser welding, is welding speed, frequency, pulse width and so on technological parameter influences to be big. In the power limit, raising the power or reducing welding speed; or increasing the frequency, or increasing the pulse width in critical value range, it be possible to increasing joints strength, however, when the pulse width surpasses critical value range its joints strength instead fall. In this study, the parameter that the appearance and the quality are all good of welded seam for welds speed 60mm/min, frequency 10Hz, pulse width 3ms, defocusing amount -1mm, the tensile strength of joints may reach 390MPa. The joints that the performance is good, its keyhole's microscopic appearance is also more complete good, but the joints that the macroscopic appearance is good, it has fine mechanical properties certain by no means. The three-dimensional observation of keyhole appearance is relatively feasible to be appraisal laser welding welded seam newest method，it is worthy discussing and carrying out.