The speed reducer with three cycloid gears, namely FA high-precision drive speed reducer, is the most advanced drive device all over the world. The speed reducer has the advantages of small size, little weight, large drive range, long service life, good rigidity, good stability and precision, high efficiency and stable drive. Compared with wave drive by robots, the speed reducer has better fatigue resistance, bigger rigidity, longer service life and higher return difference precision; the FA speed reducer is used more and more frequently in becomes the weakest part of the whole structure. The paper mainly focuses on the study of this structure. When cycloid drive adopts a large drive ratio, in order to avoid the interference of cycloid gears, the size of gears is very small so that the strength of gears is reduced, which becomes the weakness for drive. Therefore, the paper adopts the new structure of horizontal gears. The paper analyzes the force upon cycloid gears of this structure mainly by analysis, the sketch of this new structure of horizontal gears for three-gear cycloid gear.