The servo drive mechanism for a flat joint machine comprises: a feed bar (1), a feed lifting cam (2), a pin shaft (3), a socket base (4), a feeding connecting rod (5), a feeding cam (6), a upper shaft (12) drove by a servo motor (11), a lower shaft in platform (18) drove by a rotary-shuttle servo motor (10), and feed lifting shaft drove by a feed lifting servo motor (9). This invention eliminates a bevel gear structure and an engagement gear structure to reduce assembly difficulty and cost.