The invention relates to the technical field of drive devices, and discloses an upper input and lower output type speed reduction gear box. The upper input and lower output type speed reduction gear box comprises a box body, wherein the box body forms a three-stage gear speed reduction mechanism through a first-grade rotating shaft, a second-grade rotating shaft, a third-grade rotating shaft, a fourth-grade rotating shaft and gears on the shafts; a three-grade gearwheel is arranged on the fourth-grade rotating shaft; an oil baffle cover, comprising cylindrical sidewalls of which two ends are opened, is fixedly connected into the box body; the cylindrical sidewalls sleeve the outside of the fourth-grade rotating shaft; lower end ports of the cylindrical sidewalls are in sealing connectionwith the inner surface of the lower wall of the box body; a first circular ring slot is formed in the lower end of the third-grade gearwheel; upper end ports of the cylindrical sidewalls extend into the first circular ring slot. According to the upper input and lower output type speed reduction gear box, an oil baffle disc in the prior art is replaced by the improved oil baffle cover; the gear arraignment mode in the scheme enables good oil baffle effect; a bearing at the lower part of the fourth-grade rotating shaft can be lubricated through semi-solid lubricating grease, and thus the risk that liquid lubricating oil leaks from the box body is avoided.