To study the load distribution mechanism of power-split transmission and improve the carrying capacity of the gear box for herringbone star gear transmission system, a dynamics model for the geared turbofan(GTF) engine with a flexible pin was established based on finite element method. The dynamic load sharing characteristic of the system was studied in equivalent meshing error, and the influence of the error incentives, structure of pins, and working condition on load sharing characteristic was analyzed. The results show that the vibration track of the center gears deviates from the origin resulted by the eccentricity error, which is the primary cause for the inequality of load distribution. The load sharing coefficient of the system increases linearly with the error, and the influence of manufacturing errors is larger than assembling errors. The flexible pin can significantly improve the load sharing performance, and the flexible pin improved by Montestruc has best load sharing performance among the four kinds of pins. The load sharing coefficient declines with the increase of input speed, the resonance would lead to a sharp drop of loading sharing performance. The load sharing performance is improved with the increase of the input power, and the advantage of flexible pin is more prominent when the input power becomes lower.