With the development of nanophotonics, optical structures, such as optical microcavity, waveguide structure, photonic crystal, subwavelength gratings and metasurfaces, can realize light transmission and manipulation at nanoscale, which promotes the development of optical integration. Subwavelength grating has been widely studied by scientists because of its simple structure and low cost. It has gradually formed a mature theoretical system of grating analysis model when applied to various optical devices. Combined with the coupling of periodic structure and scattering modulation characteristics of meta-atoms, the metagrating derived from subwavelength gratings can improve the efficiency by using periodic Bragg scattering, thus avoiding the efficiency reduction and energy loss caused by the phase discretization. Scientists have studied and designed metagratings, and more physical phenomena and applications have been explored. In this paper, the basic theory, design and application of subwavelength gratings and metagratings were summarized. Based on the basic principle, the characteristics of subwavelength gratings and metagratings were discussed, the theoretical and unit design methods were also outlined and their applications in biosensing, spectral control of filter and absorption film were introduced. Finally, the future development was prospected.