The invention provides a circular seam lock bottom connector and a manufacturing and welding method thereof. The method mainly comprises the steps of connector design, part preparing, welding preparing, assembling and spot welding, and formal welding. The connector design mainly focuses on the problem that due to the non-penetration state of laser welding of the lock bottom connector, air holes are formed easily, a groove is designed in a lock bottom part, the groove achieves the penetration state of laser welding on the structure, and the problem of the air holes can be solved. In order to relieve the situation that due to the groove, when gas in a closed cavity is heated and swelled in the welding process, small holes of laser welding and a molten bath are disturbed, and the welding stability is influenced, a ditch is designed in the lock bottom part, the ditch can communicate with the closed cavity and the outside, when heated swelling and cooling shrinkage occur in the laser welding process, the gas in the cavity breathes freely and circulates with the outside, the gas pressure in the cavity is stable, and thus disturbance on the molten bath for the laser welding and the smallholes is avoided.