Subwavelength metal grating has special properties which the traditional grating does not have. As a kind of optical element, it has a sort of excellent performances, including high transmission and extinction ratio,wide spectrum range, great polarization properties and so on. It plays an important role in the field of applications of subwavelength optical components. Furthermore, it can reduce the optical components and increase flexibility in the optical systems due to the advantages of small volume, compact structure and easy integration. It has the potential to improve and replace traditional optical devices. This paper presents the development of the analysis theories, as well as the trends of the innovation of structures, study of multidimensional,theoretical simulation to experiment, and applicable band extending to terahertz and ultraviolet band, for the subwavelength metal gratings. It also describes the wide application prospect of the subwavelength metal grating in the fields of laser system, polarization imaging, photoelectric detection, thin film solar cells,optical sensing, etc.