Abstract: Zhangbei area has built the world′s first new energy transmission demonstration project through the four-port soft direct transmission network, and successfully realized the efficient and reliable transmission of large-scale scenic resources in Zhangbei and Kangbao areas to the concentrated areas of electricity consumption. However, as the wind farm stations are connected to the flexible and straight system, several sub/super-synchronous oscillations are caused. In order to solve this problem, the oscillation mechanism of the flexible and direct transmission system of wind farm station is analyzed. According to the requirements of the electric power research unit on the impedance characteristics of a single wind turbine, based on the above analysis, an impedance optimization method for doubly-fed wind turbines is proposed, which combines control parameter optimization and additional damping control. Finally, through RTLAB semi-physical simulation platform and impedance scanning frequency domain analysis, the effect of reshaping impedance characteristics of doubly-fed wind turbines and the effectiveness of subsynchronous oscillation suppression method are verified.