A multi-channel terahertz waveguide filter based on multimode resonance is studied. By introducing defects in terahertz periodic structure waveguide, the passband can be formed in the forbidden band range, so as to realize narrow-band filtering. The characteristics of multi-channel filter are studied by numerical simulation. The results show that the multi-channel filtering function with adjustable number of channels can be realized by changing the defect length. The number of channels can reach 10-12, and the transmittance is more than 98%. In addition, by changing the number of cycles of the waveguide structure, the passband bandwidth can be adjusted, and the narrowest bandwidth can reach 0.01 GHz. The waveguide filter has excellent performance and has the advantages of compact structure, easy integration, high transmittance, multi-channel and narrow bandwidth. It provides an important technical reference for the development of functional devices in terahertz band.