The invention provides a turnover and demoulding mechanism of a plastic suction mould. The turnover and demoulding mechanism is used for forming an inverting mechanism on a plastic suction tray, and enabling the tray to be easily demoulded. The turnover and demoulding mechanism comprises a mounting base, a movable block and a spring, wherein the movable block is hinged to the mounting base through a rotary shaft, and is turned over corresponding to the mounting base around the rotary shaft; one end of the movable block is connected with the spring, and is abutted against the mounting base through the spring; a boss is arranged at the other end of the movable block; the top surface and bottom surface of the boss are respectively parallel with the rotary shaft; the boss is used for forming and inverting; during demoulding, the movable block is turned over corresponding to the mounting base, and an included angle between the bottom surface of the boss and the vertical direction is gradually increased. The turnover and demoulding mechanism has the advantages that larger inverting size and inclining angle can be designed; when multiple trays are stacked, the number of support surfaces can be increased.