Abstract: The present invention provides a backlash-free planetary transmission device, comprising a housing (10), a power input shaft (1) and a power output shaft (8). An eccentric sleeve (2) is securely positioned on a circumference of the power input shaft (1). A fixed pin gear (5) is set on the housing (10) that is concentric with the power input shaft (1). A power output pin gear (7) is set on the power output shaft (8) in circumferential transmission fit and concentric with the power input shaft (1). An outer ring of the eccentric sleeve (2) rotatably fits with a dual outer gear (4). An outer gear (42) of the dual outer gear (4) is meshed with the fixed pin gear (5) with small teeth difference, and the other outer gear (41) is meshed with the power output pin gear (7) with small teeth difference. The pin teeth of both the fixed pin gear (5) and the power output pin gear (7) include a roller that can rotate around its own axis.