The invention provides a self-lubricating system of a power take-off device. The self-lubricating system of the power take-off device comprises a shell, a driving gear, a transition gear and an output gear. An oil groove which is filled with lubricating oil is formed in the bottom of an inner cavity of the shell, and the lower portion of the driving gear is soaked in the oil groove. An oil nozzle is arranged on the portion, corresponding to a meshing point between the output gear and the transition gear, of the shell. The output gear rotates from the lower end point of the output gear to the upper end point of the output gear by passing through the meshing point between the output gear and the transition gear. Due to the facts that the oil groove is formed in the bottom of the inner cavity of the shell, and the oil nozzle is arranged on the portion, corresponding to the meshing point between the output gear and the transition gear, of the shell, the lubricating oil is guided with the help of centrifugal force generated by rotation of the driving gear and the output gear to lubricate the driving gear or the output gear and corresponding bearings, the structure and the technology are simple, the manufacturing difficulty is low and the lubricating effect is relatively good.