The invention discloses a subwavelength grating based on bounds state in the continuum as the optical antenna for optical phased array, which includes a substrate and a grating layer atop the substrate. The grating layer includes a strip waveguide and sub-gratings symmetrically arranged on both sides of the strip waveguide. The sub-gratings may also be placed on different layers to build a multi-layer grating. The sub-grating excites the radiation modes, and destructive interference is formed between the sideward radiation modes by adjusting the width of the strip waveguide, which is used to establish the bounds state in the continuum. By designing the grating structure and adjusting the width of the strip waveguide, the invention establishes a diffraction-limited bound state in the continuum between sub-gratings to suppress sideward emission, thereby suppressing crosstalk between gratings, reducing the antenna pitch of the optical phased array, and increasing the phase-tuned beam steering range.