Based on shorten wavelength effect and lowpass characteristic of interdigital structure, a compact dual-mode narrow band BPF (band-pass filter) is proposed in the paper. This filter combines interdigital structure with conventional dual-mode BPF, and takes full advantage of the blank center of conventional dual-mode loop resonator. The shorten wavelength effect and low-pass characteristic of interdigital structure is analyzed first of all, and then a structure of dual-mode narrow band BPF using interdigital structure is proposed, followed by simulation and optimization. At last, the novel filter is fabricated and the measurement results show that the proposed filter has favorable application value due to its compact size and good performance.