Proposed are a flexible cover window for simultaneously improving strength characteristics and folding characteristics of a glass-based ultra-thin flexible cover window, and a method of manufacturing the same. A glass-based flexible cover window is configured such that a ratio of the intensity of replacing metal ions at the glass center to the intensity of replacing metal ions at the glass surface is 1:3 or greater. The present disclosure can provide a flexible cover window with improved window strength characteristics and folding characteristics by adjusting the depth (ion penetration depth) and the surface compressive stress of a tempered layer by performing a gradient tempering process including primary tempering, slimming, and secondary tempering.