A vacuum forming method for a membrane-like object having a protruding structure and its forming apparatus, the forming method includes the following steps: fixing a flat membrane having a protruding structure on a sealing device; fixing a product model on a vacuum pumping device; clamping a transfer device on the protruding structure; utilizing a heating device to heat the flat membrane for softening the flat membrane; controlling the transfer device to move the protruding structure to a predetermined forming position; fitting the sealing device tightly to the vacuum pumping device; pumping out air between the flat membrane and the product model by the vacuum pumping device to generate negative pressure, so that the flat membrane is completely attached to a surface of the product model to form a final membrane having the protruding structure; after cooling, the final membrane having the protruding structure is taken out of the cooling room.