A butt welding method for a heavy wall steel plate is adapted to perform multi-layer welding for forming a lower layer, an intermediate layer including a plurality of layers, and an upper layer in a groove, the layers each including a weld bead. The step of forming the intermediate layer includes a single-layer forming step (S1) of forming the weld bead in the groove, a cooling step (S2) of cooling the weld bead to a predetermined temperature, and a post-cooling reheating step (S3) of reheating the cooled weld bead. Furthermore, the butt welding method for the heavy wall steel plate includes a stacking step (S4) of repeating a cycle as many times as the number of layers in the intermediate layer, the cycle including the single-layer forming step, the cooling step, and the post-cooling reheating step, and thus stacking the weld beads of layers necessary for the multi-layer welding.
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