Abstract: With the development of terahertz technology, devices based on the frequency selective surface (FSS) structures, which are widely used in microwave band, are also gradually introduced to the terahertz functional devices. CST software has been used to simulate the FSS with rectangular and circular holes. Terahertz time-domain spectroscopy (TDS) has been used to measure the transmittance characteristics of FSS. Then, multi-layer FSS and medium-load FSS are simulated by CST software to explore the sensitivity of FSS.