To achieve miniaturization of Ultra-Wideband(UWB) bandpass filters, a novel interdigital filter and its design method are proposed. The filter realizes large coupling coefficient using broadside- coupled structure, and unnecessary cross coupling is reduced by widening the width of stripline resonator. It simplifies the design method of the filter. A six-pole interdigital bandpass filter is designed using the proposed structure, which is centered at f0 GHz with a fractional bandwidth of 58%, and the size of the filter is 8 mm×11 mm. The simulation results show that the filter keeps the advantages of the traditional interdigital filter with good stopband characteristics and spurious response.