The present disclosure provides a speed reduction device, a joint servo and a robot. The speed reduction device includes a driving device, a first stage speed reduction assembly and a second speed reduction assembly. The first speed reduction assembly includes a power gear and a face gear. The second speed reduction assembly includes a sun gear that rotates coaxially with the face gear, a planet gear set driven to rotate by the sun gear, a fixed gear, an output gear for outputting power and a fixed shaft. The speed reduction device uses the first speed reduction assembly and the second speed reduction assembly for power transmission and is compact in structure and has a high single stage transmission ratio.