Abstract: Resonators are introduced in traditional multimode resonators and two or more of them are used to combine and construct the filter passband. However, due to the large number of resonators, they occupy large space in the radio frequency system. Therefore, a three-mode bandpass filter based on semicircular half mode substrate integrated waveguide (HMSIW) is proposed in this paper. The electric field distribution of the resonance mode of the semicircular HMSIW resonator is disturbed by introducing a metallized via, so that the frequency of the corresponding resonance mode will also shift, and then the frequencies of the three resonance modes with large differences in the original resonance frequency will gradually approach, and finally the filter passband will be formed. It does not need to introduce additional resonators, and can reduce the filter size by half or even multiple, thus achieving the goal of miniaturization.