The invention discloses a spray cooling system of an air-cooled radiator of a large-scale steam turbine and belongs to a spray cooling pipeline system. The spray cooling system solves the technical problems that a triangular type cooling radiation unit fails to meet the design requirement of the radiating effect due to the influences of high air temperature, gale, circumfluence of hot blast and other factors. A triangular roof truss body (7) consisting of a cooling water master pipe (3), cooling water branch pipes (4) and cooling water spraying heads is arranged in a triangular type cooling radiation unit (2) of the large-scale steam turbine; the upper ends of cooling water left branch pipes (8) and cooling water right branch pipes (9) are communicated with the cooling water master pipe (3); the upper end of a set of the cooling water left branch pipes (8) is a closed end; and four to five cooling water spraying heads of the left branch pipes with movable and adjustable spraying direction are arranged on each cooling water branch pipe. With the spray cooling system, the triangular type cooling radiation unit can meet the design requirement of radiation under the condition of various working environments and improves the operating economy of a steam turbine set.