Abstract: Liquid crystal polymer ( LCP) substrate is a new generation of substrate material for microwave and millimeter-wave application after LTCC．LCP substrate features low loss，low cost，large range of frequency，high strength and light weight，etc．In this paper，the manufacturing process of LCP substrate is described in detail．The performance of coplanar transmission line based on LCP substrate is analyzed．A 21dB coupler with two layers of substrate is designed，its frequency is at X band． It lays the foundation for the research of microwave passive circuits based on LCP multi-layer substrate．