Based on the SSP dispersion curve of metal grating structure,a copper strip grating structure with uniform on one side and non-uniform on the other side with an op en in the middle is designed in this paper to achieve tight focus and field enhancement in the terahertz band.Studies show that when 0.57THz incident plane wave pass through the two- sided open metal grating,obvious local electromagnetic field enhancement and tight focusin g effect can be achieved,in which the enhancement factor Q=59.9and t he full width at half maximum of tightly focal spot is approximately 7.5μm (1/70λ).In addition,the single two-sided open metal grating was considered as a unit and arranged or extended in horizontal di mension and longitudinal dimension to generated multiple type of focusing filed.We found mu ltiple focal spots in one-dimensional can be generated when the 0.57THz incident plane wave pass through the horizontal alignment structure,and the full width at half maximum correspon ding to the multiple focal spots is about 7.5μm.At the same time,the focal line can be g enerated when 0.57THz incident plane wave pass through the longitudinal extending structure, in which the length of the focal line is approximately 100μm and width of the focal line is about 7.5μm. The multiple focal spots and longitudinal focus line generated by this periodic structure have obvious advantages in improving the speed of terahertz near-field imaging.