An improved active disturbance rejection controller (ADRC) suppression strategy is proposed to address the problem of broadband oscillation between the direct-drive wind turbine and the weak AC power grid. Firstly, the model of the direct-drive wind turbine connecting to grid is established, and the mechanism of broadband oscillation is analyzed. The ADRC design is conducted within the grid side converter. Secondly, a multi-objective optimization function is developed to tackle the difficulty of ADRC parameter tuning and improve system stability and response speed. The function includes the frequency error of the grid access and the adjustment time of the system. The parameter tuning of improved ADRC is realized by combining the method of global search and optimization to improve the rapidity, accuracy and rationality of the parameter design. Finally, MATLAB/Simulink simulations are used to compare the broadband oscillation suppression effects of controller parameters designed by the traditional bandwidth method with those from the proposed method. The overshoot, adjustment time, and harmonic content of the grid-connected current are reduced when the proposed method is applied. The results indicate that the improved ADRC strategy enables good dynamic response characteristics, noise immunity, and grid-connected current quality for the direct-drive turbine system.