In this paper, we propose a ultra-period all-dielectric grating metamaterial structure.This structure has multiple sub-cell structure in a single big perio d.By optimizing the structure parameters of the super-period grating structure,such as the duty cy cle,height and the width of the grating strip,the broadband perfect reflection is achieved with th e bandwidth of 1.2－2.0THz. Through the S-parameter inversion algorithm,the equivalent parameters of the s ub-wavelength superperiodic all-dielectric grating structure are extracted,including equiva lent refractive index, equivalent permittivity,equivalent magnetic permeability and equivalent impedan ce.By analyzing the equivalent parameters and combining the perfect reflection conditions,the p erfect reflection characteristics of the super-period grating structure proposed in this paper ar e confirmed.Based on the full-wave vector numerical simulation method,the electromagnetic field dis tribution characteristics of the super-period grating structure are calculated,and the Mie resonance characteristics and electromagnetic coupling characteristics of the broadband te rahertz perfect reflection super-period grating structure are analyzed.