With the development of double-sided laser beam welding technique of aluminum alloy T-joints for domestic aircraft fuselage panels as the ground, the effects of welding parameters and laser posture on the welding seam formation quality are studied in details, and the microstructure characteristics of the T-joints are also preliminarily discussed. The experimental results show that it can realize the welding of T-joints for aircraft fuselage panels by double-sided laser beam welding and can obtain good welding appearance. In order to get adequate weld, the heat input will be controlled between 25 J/mm and 35 J/mm by matching laser power to suitable welding speed. Moreover, the wire feeding speed must be reasonable matched to guarantee the smooth transition of the weld surface. It is better to adopt low incident beam angle under the requests of weld penetration and fusion area, which is good for reducing the heat effects of the heat input. The optimal incident beam position is determined to be 0.2 mm on the stringer yielding a 45°～50° seam angle, and the maximum tensile strength reaches a maximum value. In order to keep the double-sided weld symmetry and improve the mechanical properties of T-joints, the beam separation distances must be strictly controlled to realize the double-sided welds fused in a common molten. Five distinct zones are identified which consist of the cellular dendrite zone, parallel dendrite zone, partially melted zone, over-aged zone, and base material. The partially melted zone become narrower further from the fusion zone center and which on the skin side is obviously than that on the stringer side.