To study the oscillation mode of GTA weld pool, the oscillation mode of weld pool was analyzed based on Bessel equation, and the laser dot matrix images of (0, 1), (1, 1), (2, 1), (0, 2) oscillation modes at different times are obtained by structured laser optical measurement simulation. The oscillation mode of stationary GTA weld pool was analyzed based on the laser dot matrix images obtained by structure laser experiment. The result shows the simulated laser dot matrix images matches up to the experiment result. The oscillation mode of the weld pool can be recognized based on laser dot matrix image. This study can not only provide conditions for judging the penetrating state of weld pool, but also help to further understand the oscillation mode of the weld pool and develop more effective observation methods and measurement tools, so as to effectively control and improve the welding quality.