Planetary gears are in effect declared as a compact design solution for the transformation of mechanical energy,with large capacity per unit mass and high transmission ratio. Following the disadvantages of such solutions is the need for replacement of all the gears in the set, in a case of damage in one of the planetary gear sets. Usability of these and other parts is uneven. Besides that, there are some specific details in determination of the reliability of the planetary gear. In this paper was developed a specific approach for determining the reliability of the planetary gear, and for the development of rational design solutions of this type. It was also elaborated the procedure of applying the Weibull’s probability function for presenting the wear of gear teeth.