The invention discloses a folding and unfolding mechanism. The folding and unfolding mechanism is installed between an upper panel and a lower panel which are hinged and used for folding and unfolding the upper panel and the lower panel and completing overturning at 0-180 degrees between the upper panel and the lower panel. The folding and unfolding mechanism comprises a four-connection-rod assembly, a push rod assembly and an auxiliary connection rod assembly. The auxiliary connection rod assembly comprises a first auxiliary connection rod and a second auxiliary connection rod. One end of the first auxiliary connection rod is hinged to one end of the second auxiliary connection rod. The other end of the first auxiliary connection rod is hinged to the lower panel. The other end of the second auxiliary connection rod is fixedly connected with a fourth connection rod. An axial locking mechanism is added, the included angle relative to the axis of an oil cylinder is locked after a start skid acts to the preset position, the start skid produces no relative rotation, the relative structure is simple, and maintenance is convenient.