Small-signal stability auxiliary decision-making is the method that determines the online power generation adjusting actions according to the results of state estimation and the parameters of element model in order to improve the damping of the weekly damped mode to assigned security to damp the low-frequency oscillation. In this method， participation factor is adopted as the performance index to adjust power generation so as to avoid extra calculation time; generators are divided into two clusters based on the angle of mode shape and the adjusting direction of two clusters is confirmed by power perturbation method; the corresponding damping mode after generation adjusting is ascertained according to the frequency and cluster information; the direction of generation adjustment actions for coordinated control is determined by the participation factors and the direction of generation adjustment actions of different modes， and sensitivity method is used to determine the generation adjustment actions for a single mode; the merged actions are corrected through a range given eigenvalue calculation in order to validate the control actions， then the generation adjustment actions for coordinated control of multi-weekly damped modes can be obtained. Applications in a real large power grid verify the proposed method.