A novel polarization-insensitive metasurface with angular stability for ultra-broadband (from 7 to 12 GHz) backscatter radar cross section (RCS) reduction is investigated. The proposed metasurface is composed of carefully arranged unit cells with spatially varied dimension, which can diffuse reflection uniformly and avoid the reflection in the specular direction. A proposed metasurface sample is fabricated and tested to validate RCS reduction behavior predicted by full-wave simulation software ANSYS HFSS. A more than 10 dB RCS reduction within the entire X-band is observed, indicating our metasurface may be potentially applied to future stealth technology.