In this study, a terahertz metasurface label based on a frequency-selective surface (FSS) was designed. The overall structure is composed of a surface metal pattern, intermediate medium, and a bottom metal plate. The structural unit of the FSS consists of symmetrical octagonal nesting rings etched onto an intermediate polyimide medium. When a nested ring disappears, the absorption peak of the corresponding resonant frequency point disappears through different coding. Effective bandwidth utilization is also achieved through frequency coding. The simulation results show that the proposed structure achieves a 4 bit coding capacity, with a working frequency range of 0.1~0.5 THz and a label area of only 0.25 mm². The proposed structure has a high coding density, the angular stability is ≥45°, polarization insensitivity is present, the requirements of label recognition accuracy are satisfied, and the coding performance is strong. In addition, a frequency shift coding rule is proposed, which introduces a frequency shift by changing the resonant structural parameters to increase the coding capacity and label coding density without changing the label volume, which can satisfy the practical application requirements more flexibly. The metasurface-based flexible terahertz tag proposed in this study is different from the popular RF tag and has strong application prospects for miniature objects, such as medical and industrial components, automotive parts, and silicon chips.