Filter is the core communication device in optical integrated chip. In recent years, plasma-induced transparency in surface plasmon (SPP) subwavelength waveguide photonic deviceshas become a research hotspot in the field of nano optics. The plasmon-induced transparency (PIT) is a phenomenon that the original absorption region produces a sharp transparent window due to the interaction among different resonant modes of SPPs, therefore, a higher resolution and quality factor surface plasmons can be obtained by using this feature to design a metal-medium-metal (MIM) waveguide structure filter. However, due to the Ohmic loss caused by metal parts, further research is needed on how to effectively improve transmission efficiency and achieve better frequency selection and filtering effect while reducing filter bandwidth in MIM waveguide filter. Based on the transmission and coupling characteristics of SPPs, an MIM waveguide filter with semi-closed T-waveguide side coupled disc cavity is proposed.Its transmission characteristics are studied by using the finite element method. The results show that a narrow-band transmission peak based on plasma-induced transparency appears in the transmission spectrum. Through theoretical analysis and mode field distribution, the physical mechanism of generating the PIT transparent peak and valley values on both sides is effectively explained. Compared with the traditional straight waveguide structure, the curved waveguide structure can generate the bilateral coupling effect, which can make resonant interaction stronger. Meanwhile, the numerical study shows that the approximately linear adjustment of filter wavelength can be achieved by changing the length of branches, the radius of the disk cavity and the refractive index of the medium in the cavity through external modulation. Further, the gain medium is embedded in the disk cavity, which enhances its local ability to emit light, strengthens the mode resonance effect, and realizes the compression filter pass-band bandwidth while effectively improving the structural transmittance, compared with similar filters. The research results provide an effective theoretical reference for designing the high resolution narrowband filter.