The invention discloses a preparation method of a flexible copper-clad liquid crystal polymer substrate. First, a layer of LCP glue is coated on a layer of copper foil, and then dried in a tunnel oven, and then the obtained copper foil with an LCP glue layer is The foil is laminated with another layer of copper foil to obtain a substrate, which is then post-cured in a programmed oven to obtain a flexible copper-clad liquid crystal polymer substrate. Through this method, the thickness of the LCP adhesive layer can be easily made ultra-thin, which is conducive to the development of ultra-thin electronic products in the future, and the low-temperature press is used to replace the high-temperature press during lamination, which greatly reduces the cost and improves the production capacity. It has also been improved, and the post-curing step is performed on the laminated substrate to effectively eliminate internal stress, improve the bonding strength and cohesive strength, and improve the strength of the entire flexible copper-clad liquid crystal polymer substrate.