The invention discloses a computing method for improving small signal stability and providing aid decision making, which is suitable for computation of output power adjustment measures of units for improving a plurality of dampers in weak damping modes under the determined mode of operation. The method is characterized by considering the weak damping modes and the modes close to safe damping threshold while determining the coordination control properties of the units, selecting the units with larger participation factors in the weak damping modes to participate in output power adjustment, dividing the units participating in output power adjustment into two groups according to the unit mode information in each mode, determining the output power adjustment directions of the two groups of units by a method of perturbation of power, determining the output power adjustment directions during coordination control by combining the participation factors and the output power adjustment directions of the units in different modes, computing the output power adjustment measures of the units for improving the dampers in the single mode by a sensitivity method, checking the combined control measures by computing the eigenvalues in the given range to determine the effectiveness of the control measures and giving the output power adjustment measures of the units for coordination control of a plurality of weak damping modes.