Double-sided fiber laser beam welding is used to synchronously weld T-section of fuselage panels (skins and stringers) for aluminum-lithium alloy 2060/2099 and shaping control is analyzed as well as long transverse (LT) tensile performance. The results indicate that a good fusion between skins and stringers can be obtained by using incident beam angle as small as possible in an adjustable range. The LT tensile strength reaches the maximum when the incident beam position is 0.1 mm on the stringer yielding a 45°~50° weld beam angle. To ensure weld microstructure uniformity and improve the T-joints′ mechanical properties, beam separation distance must be strictly controlled to achieve the fusion of the double-sided welds in a common molten. In order to realize smooth transition of the weld surface, the ratio of wire feeding speed to welding speed should be matched with a reasonable value. For welds with a fully fusion and uniform microstructure, the key factor restricting the LT tensile strength is weld penetration. The average LT tensile strength reaches 80.1% of that of the base materials and the maximum rises up to 82.1%, when weld penetration is controlled in 1 mm.