Abstract: A finite element model for double-sided TIG backing welding of thick plate was established, and the reasonableness and accuracy of the model were verified by welding experiments. Then, the temperature fields in backing welding thick plate were simulated for different groove designs with different sizes of misalignment and root face, respectively. The results show that, with the increase of the reserved groove gap, the allowable range of root face increased using double-sided TIG backing welding, and the allowable range of misalignment increased first and then decreased. In backing welding of thick plate, when the sum of root face and misalignment was less than 4 mm, the weld with good root fusion could be obtained with reserved 2-4 mm groove gap. When the sum of root face and misalignment was more than 6 mm, incomplete penetration occurred. When the sum was between 4 mm and 6 mm, the root fusion changed with the reserved groove gap.