Method and mould for forming optical element with microstructure

The invention provides a forming method for optical element with micro structure and forming mold. The method is: it provides a mold, and forms a mold cavity in the mold, arranges a pouring aperture connected to the mold cavity at front of the mold cavity; the mold cavity is formed into a closed space; there has at least an air extracting aperture near the end of the mold cavity in the space, and fills the mold cavity through the aperture; and fills the material into the mold cavity to be formed, in order to acquire the optical element with micro structure. The invention uses the gap between the upper mold and the subjacent mold, and between the upper mold core or the subjacent core to extract the air in the cavity, it can reduce the waste generation, and it can upgrade the quality of the product.