In order to realize terahertz tunable filtering wave, a terahertz tunable filter based on flexible materials was designed. By twisting the Teflon waveguide to form a ring resonator, the band-stop filter function in the 160 GHz to 200 GHz frequency band is realized. Changing the length of the resonant cavity can achieve the tuning of the free spectral range (FSR) and the filtering frequency. In the experiment, the switching of the free spectral range between 1.9 GHz and 2.8 GHz and the corresponding filtering characteristics are tested. Research results show that when the length of the resonant cavity is fixed, the stopband can be adjusted by changing the bending radius. The terahertz ring resonator using flexible materials can be used for tunable filtering and has a higher degree of freedom.