In this paper, a 4-bit reflective coding metasurface with the polarization-insensitive unit cell is designed for wideband radar cross section (RCS) reduction. The metasurface unit has rotational symmetry; therefore, it produces the same electromagnetic scattering response for both xand y-polarizations. To attain 4-bit phase response, the dimensions of the unit cell are optimized so that a phase difference of 22.5° is realized between respective digital elements and the magnitude of reflection is more than 0.95 from 15 GHz to 40 GHz. Therefore, 16 digital elements have phases of θ, θ + 22.5°, θ + 45°, θ + 67.5°, θ + 90°, θ + 112.5°, θ + 135°, θ + 157.5°, θ + 180°, θ +202.5°, θ +225°, θ +247.5°, θ +270°, θ +292.5°, θ +315°, and θ + 337.5°. Discrete water cycle algorithm (DWCA) is applied to the array factor to get the optimal coding sequence matrix for better RCS reduction. The coding metasurface can achieve more than 10 dB RCS reduction from 15 GHz to 40 GHz as compared with the same size of a copper sheet. The simulation and experiment results validate the ability of proposed coding metasurface for robust control of EM-wave and wideband RCS reduction.