Load sharing among planetary gears, one of the design variables, has a significant influence on the performance and service life of a gearbox. This study involved simulating and testing the design parameters related to load sharing among planetary gears. In this regard, the influence of errors in the carrier pinhole position on the load sharing among the planetary gears was analyzed. The results showed that the difference between the simulation results using the model and the laboratory test results was less than 10%. Furthermore, similar tendencies were observed according to the magnitude of the load applied to the planetary gears. As for the design parameters affecting load sharing, the service life of a gearbox containing planetary gears can be extended by using a floating system as opposed to a non-floating system. In addition, reduced planetary pin diameter and increased planetary bearing clearance leads to appropriate load sharing among the planetary gears and increases the service life and floating effect of the gearbox.