Abstract: In the installation process of wind turbine, the bottom T-flange plays the role of connecting the tower and the ground foundation pile, and is an important part of connecting the fan, which directly affects the installation and operation life of the fan. In production, the welding of the bottom tower door hole and door frame has a great influence on the flatness of the T-flange. This paper discusses and analyzes the influence of door frame welding on the ellipticity of the bottom T-shaped flange, preventive measures and solutions.