Abstract: In order to study the effect of different welding parameters on dynamic changes of weld pool of lap joint of 304L stainless steel sheet in MARKIII type LNG ship enclosure system, the coupling model of temperature field and flow field of pulsed plasma arc lap angle weld was established, the inclined double ellipsoid moving heat source was adopted, and the effect of electromagnetic force, arc pressure, buoyancy and surface tension on the weld pool was considered, and the effects of peak current and welding speed on the weld pool characteristics of the lap joint were analyzed. The results show that the temperature distribution of the lap joint weld pool under the action of the inclined heat source is asymmetric, and the flow field of the weld pool generates asymmetric vortices. When the duty cycle and the base current are unchanged, the peak current is proportional to the heat input, and the width of the weld pool, the width and depth of the weld pool on the bottom plate increase with the increase of the peak current. The welding speed is inversely proportional to the heat input, and the weld width, bottom plate weld width and bottom plate weld depth decrease with the increase of welding speed. The simulation results are in good agreement with the test results, the simulation process is accurate and reasonable, which provides a basis for obtaining good quality weld forming.