A high-uniformity multichannel plasmonic filter based on metal-insulator-metal (MIM) waveguide is proposed. It consists of two metal layers and sandwiched multiple insulator super units structured by alternately stacking two insulators with different refractive indices. By linearly lengthening the high refractive index insulators in each super unit, the dispersion-induced loss coefficient can be reduced and flattened, leading to a high uniformity among multiple transmission channels of the plasmonic filter. The corresponding spectral characteristics are numerically investigated by using the finite-difference time-domain method. Fourteen transmission channels with an excellent channel uniformity of ±0.2 dB and a peak-to-notch contrast ratio greater than 14.8 dB in the range of 1-2 μm, have been confirmed.