Abstract In this paper, the plasmonic band-stop filter with unilateral multi-tooth structure and the causes of Fano resonance are studied theoretically and numerically. Fine-tuning of the bandwidth and center wavelength can be achieved by varying the spacing and tooth depth between the tooth cavities. This phenomenon can be attributed to the interference superposition of reflected and transmitted waves from each tooth cavity. When the spacing between the tooth cavities changes, the position of the formant in the transmission spectrum changes as the resonant wavelength of the cavity changes. In the case where only the depth of the tooth is changed, the length of the red shift of the center wavelength of the band stop is almost twice as large as the depth of the tooth. The finite difference time domain method is used to simulate and calculate the coupling of surface plasmon waves of different structures in this paper. The plasmonic waveguide band-stop filters we propose here may have meaningful applications in ultra-fine spectral analysis and high-density nanoplasma integration circuits.