The invention relates to a folding rotating shaft and a folding vehicle-mounted table board, and belongs to the technical field of vehicle-mounted accessories, the folding rotating shaft comprises a first fixed support, a second fixed support, a movable support and a rotating shaft, the first fixed support is provided with a first placing groove, and the second fixed support is provided with a second placing groove; the first placement groove and the second placement groove jointly form a containing space, the first fixed support and the second fixed support are embedded into the opposite sides of the two folded table plates respectively, the movable support is placed in the containing space, two rotating holes are formed in the movable support, and the two rotating shafts are arranged in the first placement groove and the second placement groove respectively. The rotating shaft is sleeved with a plurality of elastic pieces, the rotating shaft penetrates through the corresponding rotating holes, the elastic pieces are located in the rotating holes and abut against the inner wall of the movable support, and the movable support can rotate around the rotating shaft. The folding rotating shaft has the advantages that the abrasion degree is low, the service life of the folding rotating shaft is prolonged, and it is ensured that the durability and attractiveness of a product can be greatly improved.