Abstract: In order to carry out welding distortion prediction of large scale thick plate welded platform structure, a mock-up was welded first using actual welding process, during which angular distortion induced by welding was measured. And then welding numerical simulations of mock-ups having actual number of bead and lumped number of bead were conducted to verify the accuracy of the relevant input parameters of welding FE model and the reasonableness of the lumped-weld scheme by comparing their angular distortion results. Finally, welding FE model of the platform was established based on the scheme of lumped-weld, and welding induced distortion of the structure was analyzed. The results shows that the angular distortions of FE model and lumped-weld FE model are both similar to the test value of the mock-up, which is about 1.6°. That is to say the accuracy of the lumped-weld scheme that simplifies the 15-layer 27-pass in actual welding process to 5-layer 5-pass was verified. The welding distortion of the platform structure is localized falling or convex outward deformation resulting from welding angular distortion caused by the asymmetry of the upper and lower grooves and the support effect of the bottom steel frame. The surface outward deformation range is about −5.2 to 4.4 mm.