The invention discloses a special high-power worm-gear speed reducer for photo-thermal generating tracking, comprising a big gear box, a big worm wheel and two big worm screws, wherein the two big worm screws are symmetrically arranged at the left side and the right side of the big worm wheel; each big worm screw is provided with a small worm wheel; the small worm wheels are respectively providedwith a small worm screw; the end parts of small worm screws are respectively connected with a stepping motor; the stepping motors output power and moment to the outside by the small worm screws, the small worm wheels, the big worm screws and the big worm wheel in sequence after the stepping motors rotate; the big worm wheel is arranged and positioned in the big gear box by bearings; the two end faces of the big worm wheel are respectively provided with a flange output disk; and the flange output disks are used for directly connecting with loads. In the invention, an axle-free output speed reducer is utilized; and worm wheels are transmission parts and also output parts, and provided with two functions of the transmission parts and the output parts. Because wheel gears are hollow and a flange type output mode is adopted, thus greatly lightening the structural weight and reducing the number of the parts, simplifying the design, and improving the working precision and efficiency.