The invention relates to the field of machining, in particular to a lug folding mechanism for a metal plate punching and lug folding machine. The lug folding mechanism comprises a base plate and a machining table, the base plate is fixed to the machining table, the base plate is provided with a second sliding plate, and the front end of the second sliding plate is provided with a pressing block moving up and down; the position, behind the pressing block, of the second sliding plate is provided with pre-bending blocks moving up and down, the front ends of the pre-bending blocks are provided with openings, the pre-bending blocks are provided with a row of inserting needles moving up and down, and the pre-bending blocks are internally provided with jacking blocks moving horizontally; the front end of the base plate is provided with a hanging rack, the top of the hanging rack is provided with an installation frame, the top of the installation frame is provided with a pressing air cylinder, the two sides of the installation frames are provided with guide rails, the pressing block is in sliding fit with the guide rails, and the output end of the pressing air cylinder is fixedly connected with the top of the pressing block. By means of the lug folding mechanism, rapid forming of a workpiece folded lug is achieved, operation is simple, excessive participation of manpower is not needed, and production efficiency can be effectively improved.