Abstract: Liquid crystalline polymer (LCP) is used in passive circuits design and electronic package based on its perfect high frequency performance. In this paper, a compact substrate integrated waveguide (SIW) bandpass filter with center frequency of 20 GHz, fraction bandwidth 30%, and better than 2 dB of insertion loss is designed and implemented by using LCP technology. The perturbation of metallic via holes in the vertical direction of short side of the SIW is introduced in this resonant cavity, and the resonant mode is shifted from 16 GHz to 23.7 GHz as the number of metallic via holes increase,and filter performance is obtained by using a single cavity. The slot line loaded in center is used to improve the performance of filter, and the insertion loss is lower than 2 dB with little fluctuation is obtained. Meanwhile, the flexible performance is determined in detailed, and the measured results indicate that the filter have excellent transmission performance.