Based on the error and the actual tooth surface modification, a dynamic mechanics model of dual power split transmission system is established. The concentration of quality standard is used to establish the bend-torsion coupling dynamics differential equation of the system, and the equation is solved to get the frequency domain and time domain responses of the system. The results show that: through a combination of the real tooth surface fitting and the loaded tooth contact analysis (LTCA) technology, the more accurate mechanical properties of gear in different working conditions and tooth surface conditions can be gotten; the gear tooth modification can reduce the transmission error, improve the tooth surface contact, and significantly reduce the dynamic load fluctuation of the system.