Compression resistance experiment was carried out with water on tank bulkhead which was welded by friction stir welding(FSW) on longitudinal weld and by variable polarity tungsten inert gas welding(VP-TIG) on orbicular weld, and the strain brought by press was measured on typical weld position. The result shows that the intersection of FSW and VP-TIG weld has lower yield strength, which enters into the plastic deformation state at first, is the weak position of the tank bulkhead.