The invention belongs to the technical field of robots, and discloses a robot precise joint speed reducer. The robot precise joint speed reducer comprises a power module, a primary torque transmissionmodule, a secondary torque transmission module, a gear transmission detection module, a central control module, a wireless signal transmission module, a storage module, an electric power module and an alarm module. According to the robot precise joint speed reducer, the front surface and the back surface of an eccentric gear assembly are engaged with the contact print through a collection micro camera, the collected contact print image is denoised through an image processing unit, the collected front surface and the back surface of the eccentric gear assembly are engaged with the contact print through an image measurement unit to be measured and recorded, the processing result is compared and analyzed with a preset threshold value, so that the transmission error and the abrasion state ofmeshing of a rigid gear and an output shaft can be found in time, precision control is facilitated, and by means of the machining method of the eccentric gear assembly, the machining precision of therigid gear can be improved, and the service life is prolonged.