Abstract: Each block for assembling QTT antenna track is about 4 000 mm × 600 mm × 200 mm. To fabricate the track with multi-pass welding technology, it needs large groove dimension and a great amount of deposited metals, resulting large welding angle distortions. To validly predict and control the deformation, a thermal-elastic-plastic finite element model was used to simulating a scaling experiment plate considering gravity boundary condition at first. Then, another welding simulation for the actual track block structure was computed to compare with the modified formula for the welding angle distortion adding the bending moment of Gravity. The result shows that the effecting of gravity for QTT multi-pass welding was ineligible, which make the formula more accuracy.