Abstract: In terms of mechanical loads of the wind turbine generator system（WTGS）with the additional damping control（ADC）,modeling and analysis on mechanical loads are carried out for the WTGS considering machine-grid coupling. FAST associated with Matlab/Simulink is used to establish the mechanical-grid coupled model for the loads of the grid-connected WTGS,which takes into account both mechanical and electrical characteristics. Impacts of ADC on mechanical loads of the WTGS with ADC are simulated and investigated through the established model. And the resonance phenomenon between the WTGS mechanical system and the power system is recurred through the model. Results show that,the established model can effectively reflect the coupling interaction between the power system and the mechanical system in the WTGS under ADC,and the low-frequency oscillations of the power system lead to remarkable vibration loads in key WTGS structures,and when the natural vibration frequency of mechanical structures and the power system oscillation frequency approach to each other there is a sharp increase in vibration loads of a WTGS due to their resonance.