Abstract: A flexible mechanism-based anti-backlash device for a planetary gear train, a gearbox, and a robot joint are provided. The anti-backlash device includes an integrated flexible planet carrier, an adjusting screw and a spring, the integrated flexible planet carrier is provided with a moving platform, the moving platform is provided with a spring hole, and the spring is sleeved outside the screw and is installed in the spring hole; when the threaded connection depth of the adjusting screw and the integrated flexible planet carrier reaches or exceeds a set depth, the adjusting screw can extrude the spring to make the moving platform generate elastic movement along a radial direction of the integrated flexible planet carrier, and the radial elastic movement is transformed into circumferential elastic rotation of a planet carrier bearing hole around the center of the planet carrier through an elastic connector.