Abstract: In this research, an all-dielectric terahertz metasurface based on bound states in the continuum (BIC) is proposed. Each structural unit of the metasurface consists of two rectangle blocks with square cross-sections and a substrate. The substrate material is quartz, and the rectangle block material of the surface is lossless silicon. The symmetry of the metasurface is broken by tchanging the cross-section area of the rectangle block, and the quasi-BIC is excited. The resonance with extremely narrow linewidth is obtained. The transmission spectra with different asymmetric, structural and material parameters are studied using finite element method (FEM) and control variable method. Meanwhile, the Q factor of the proposed metasurface is calculated, which can reach 1.1006×10⁴ and is higher than the Q factors from related listed references. In addition, this study is aimed at the limitations of the relatively limited research on the equivalent parameters of all-dielectric metasurfaces, the S-parameter extraction method is utilized to calculate and analyze the equivalent parameters of the proposed metasurface and the physical properties of the metasurface is studied from this perspective preliminarily.