The invention relates to a special rib tire for a cross-country vehicle. A tire crown surface comprises a longitudinal drainage ditch, S-shaped transverse drainage ditches, arc transverse drainage ditches, internal rib blocks and external rib blocks, wherein the longitudinal drainage ditch is positioned on a tire crown; the S-shaped transverse drainage ditches and the arc transverse drainage ditches are alternately arranged in a crossed way; the internal rib blocks and the external rib blocks are symmetric with a longitudinal central axis of the tire crown as a symmetric axis and arranged in a crossed way; the crossed distance between the two adjacent transverse drainage ditches positioned on the two sides of the longitudinal drainage ditch is half of the longitudinal length of a transverse drainage ditch group; and the longitudinal drainage ditch is respectively in communication with the S-shaped transverse drainage ditches and the arc transverse drainage ditches. The special rib tire for the cross-country vehicle can sufficiently break water surfaces; the tire is prevented from skidding in rainy days; excellent mud throwing and drainage capacity is obtained; the special rib tire is suitable for severe muddy roads; the grip to slippery grounds can be enhanced; the heat radiation capacity of the tire is improved; pebbles are prevented from being blocked in the tire; the service life of the tire is prolonged; and the resonance noise of the tire is reduced.