The invention discloses a device and a method for welding high steel grade and large wall thickness pipeline steel. The device for welding the high steel grade and large wall thickness pipeline steel is mainly composed of a work platform controller 1, an idler wheel support 2, a work piece 3, a welding gun 5, a wire feeding nozzle 7, an ultrasonic tool head 8, an amplitude variation pole 9, an ultrasonic transducer 11, a welding power source 20, an ultrasonic generator 21, a wire feeding mechanism 22, an oscillator 14, a transmission shaft 15, an angle adjustor 16 and the like. The method for welding the high steel grade and large wall thickness pipeline steel includes: (1) placing the work piece on the idler wheel support, and starting the work platform controller; (2) setting welding voltage and a welding current, turning on the welding power source, and starting the ultrasonic generator after an electric arc is stabilized; (3) adjusting angles of the welding gun through the angle adjustor; (4) starting the oscillator, and driving the welding gun to swing back and forth through entrance and exiting movements of the transmission shaft; (5) starting the wire feeding mechanism, and staring automatic welding. The device and the method for welding the high steel grade and large wall thickness pipeline steel achieve high welding quality, good weld joint formation, and a high welding joint microstructure constituent homogenization degree, and have a broad market application prospect.