The invention discloses a half-bridge welding device capable of realizing automatic centering and clamping. The half-bridge welding device capable of realizing automatic centering and clamping comprises a base plate, a left-side welding mechanism and a right-side welding mechanism which form left-right symmetry about the base plate, a left-side centering and compression mechanism and a right-sidecentering and compression mechanism, and a left-side bridge shell compression mechanism and a right-side bridge shell compression mechanism, wherein the lower ends of a left vertical column and a right vertical column are fixed to the base plate; the upper ends of the left vertical column and the right vertical column are fixed to a lower fixed plate and an upper fixed plate separately; a slide plate is slidably connected with the left vertical column and the right vertical column; a piston rod of a pressing cylinder is fixed to the slide plate; the pressing cylinder is fixed to the upper fixed plate; the left-side centering and compression mechanism and the right-side centering and compression mechanism are fixed to the slide plate, and used for centering and clamping a bridge pipe simultaneously; the slide plate is used for compressing a bridge shell by being elastically connected with the left-side bridge shell compression mechanism and the right-side bridge shell compression mechanism; an electric rotary table is fixed to the base plate; and the left-side welding mechanism and the right-side welding mechanism are fixed to the electric rotary table, and used for welding for thebridge pipe and the bridge shell. Simultaneous clamping for the bridge pipe and the bridge shell, and location for the bridge pipe are realized through the pressing cylinder; and a welding machine mechanism realizes automatic welding for the bridge pipe and the bridge shell in the circumferential direction, and is convenient to popularize and use.