In the invention, in order to realize single-channel multi-layer welding of automatic welding, a 3 V groove is adopted on a main pipeline of which the wall thickness is more than 85 mm, and twice closing is performed during the automatic welding so as to ensure that the width of the top welding bead is not less than 10.5 mm. The invention relates to a groove for the automatic welding of a nuclearpower station and an automatic welding method, wherein the groove comprises an upper groove, a middle groove and a lower groove; the bottom of the upper groove is connected with the top of the middlegrove; the bottom of the middle groove is connected with the top of the lower groove; the bottom of the lower groove is provided with a protruding bottom truncated edge; the height of the bottom truncated edge is between 1.5 and 2.5 mm; the width of the bottom truncated edge is between 3 and 3.5 mm; the width of the top of the upper groove is between 9.5 and 10.5 mm; the width of the top of the middle groove is between 8.0 and 9.0 mm; the width of the top of the lower groove is between 6.5 and 7.5 mm; the height of the lower groove is between 12 and 18 mm; and the height of the middle groove is between 45 and 55 mm. In the invention, in order to realize the single-channel multi-layer welding of the automatic welding, the 3 V groove is adopted on the main pipeline of which the wall thickness is more than 85 mm, and the twice closing is performed for the automatic welding so as to ensure that the width of the top welding bead is not less than 10.5 mm.