<p>Planet pin position error is a critical geometric quality characteristic that significantly influences key attributes of planetary systems, including power density, load sharing, and operational reliability. Its tolerance parameters are among the key design factors determining the fatigue reliability of planetary systems in large wind turbines. In order to analyze the mechanism of these errors on the fatigue reliability of wind turbine planetary systems, a fatigue reliability evaluation model is established based on an extension of the computational logic of the full probability formula. It considers the failure correlation among the gear teeth and the temporal sequencing of the gear teeth meshing. Starting from balancing the contradiction between evaluation accuracy and evaluation costs, a hybrid finite element simulation including planet pin position errors and planet carrier flexibility, and an accelerated lifetime test for tooth probabilistic lifetime transformation are employed to respectively provide load and strength input variables for the reliability model. In particular, the Monte Carlo method is incorporated in the simulation and analysis process to take into account the randomness of planet pin position errors and the coupling influence mechanism between the error individuals. Finally, a mapping relationship from the planet pin position tolerance to the fatigue reliability of the planetary system is established. Depending on the specific reliability requirements, the upper limit of the planet pin positional tolerance zone can be determined at an early stage of the design in order to achieve as much as possible a balance between the service reliability of the planetary system and the manufacturing economy.</p>