The invention discloses a module cell string and bus bar welding positioning mechanism and a method, and a stitch welder. The module cell string and bus bar welding positioning mechanism comprises a frame, and a conveying unit, a lifting unit, an adjusting unit, a picture taking and detecting unit and a control unit which are fixed on the frame. The picture taking and detecting unit includes a picture taking unit and a light supplement unit. The picture taking unit takes an actual position picture of the end of a cell string of a module to be welded on the conveying unit. The control unit makes a comparative analysis of the received actual position picture and a pre-stored standard position picture, and makes the adjusting unit correspondingly adjust the position of the module to be welded according to the result of comparative analysis. According to the invention, the control unit makes the conveying unit convey glass and a cell string to a pre-welding station, the adjusting unit carries out coarse positioning, the picture taking and detecting unit takes a picture of a cell at a pre-welding position, and image processing and operation are carried out through a computer. Thus, the positions of the welding strip of a cell string and a bus bar can be aligned accurately in automatic welding, and the welding quality of automatic welding equipment is ensured.