A method for manufacturing a grating, a grating manufactured by the method, and an optical waveguide including the grating are provided. The method includes the following. A substrate is provided. A mask layer is formed on a surface of the substrate according to a target pattern structure of the grating, where the mask layer has a pattern structure complementary to the target pattern structure, and the pattern structure includes multiple protrusions and multiple recessed regions. A grating is formed by depositing a semiconductor material on the surface of the substrate. The semiconductor material is deposited in the multiple recessed regions of the pattern structure of the mask layer to form the target pattern structure. The mask layer is removed by lift-off. The method provided herein is simple in process and can enhance production efficiency. The manufactured grating has a relatively high refractive index and can reduce light scattering.