The invention discloses a casting high-boron high-speed steel for manufacturing a composite roll ring roller and hot processing method thereof. The steel is a wear-resistant material having superior thermal-shock resistance, and can be applied to other suitable working conditions. The chemical compositions of the steel are (weight%): 0.20 to 1.10 of C, 1.0 to 2.5 of B, 3.0 to 5.0 of Cr, 0.5 to 0.9 of Si, 0.6 to 1.3 of Mn, 2.0 to 10.0 of V, 0.5 to 1.5 of Ni, 1.0 to 4.0 of Mo, 0.2 to 4.0 of W, 0.1 to 2.0 of Nb, less than 0.04 of S, less than 0.04 of P and residue of Fe. The hot processing method includes annealing, quenching and 2 to 3 times of temper. The annealing heating temperature is 800 to 860 DEG C, furnace cooling or air cooling is carried out after furnace cooling to less than 500 DEG C; the quenching heating temperature is 1020 to 1150 DEG C, wind cooling or air cooling is carried out thereafter; 2 to 3 times of temper are carried out, the heating temperature is 500 to 550 DEG C, furnace cooling or air cooling is carried out thereafter. Compared with traditional high-nickle-chrome-molybdenum roller, the roller of the invention greatly improves alloy wearing resistance, heat resistance and thermal-shock resistance, and reduces thermal endurance crack phenomena appearing during use, as well as pits and crack arising therefrom, embodying good organic combination of safety and wearing resistance.