The invention discloses a composite welding method for a full penetration T-shaped joint of high-performance weather-resistant bridge steel, and belongs to the technical field of welding of the long-span, heavy-load, high-strength, high-toughness and high-weather-resistance bridge steel. According to the key points of the technical scheme of the composite welding method, a base material of the bridge steel with tensile strength being greater than or equal to 810 MPa has the mechanical performance characteristics that the yield strength ReL is greater than or equal to 690 MPa, the tensile strength Rm is greater than or equal to 810 MPa, the elongation A is greater than or equal to 14%, and the impact energy KV2 at minus 40 DEG C is greater than or equal to 120 J; a groove adopts a K-shapedasymmetric groove, the groove angle is 50 degrees, and the truncated edge is 2 mm; and gas shielded welding is adopted for priming of two layers firstly, and then submerged automatic arc welding is conducted to fill the cover surface. The composite welding method for T-shaped joints of different thick plates is adopted to achieve the effect that under the situations that preheating is conducted to80-100 DEG C before welding, and no heat treatment is conducted after welding, the welded joint with good weld formation and mechanical performance indexes meeting the design requirements is obtained; and the high-performance weather-resistant bridge steel can be used for construction and manufacturing of steel bridges, and the impact energy KV2 at minus 40 DEG C in all areas of the joint reaches94-138 J.