The invention discloses a voltage stability margin-based power generation rotation spare capacity optimization method. The method comprises the following steps that: 1) the operation mode of a power grid is determined; 2) the critical power transmission section of the power grid and the power transmission limit of the critical power transmission section are obtained, static voltage stability analysis is performed on the power transmission limit of the critical power transmission section, so that the voltage stability margin of the power grid can be calculated; 3) the change quantity of the voltage stability margin of the power grid, which is corresponding to the change of the rotation spare capacity of a rotation spare power generation set is calculated, the optimization plan of the rotation spare capacity is formulated according to the change quantity of the voltage stability margin of the power grid which is corresponding to the change of the rotation spare capacity of the rotation spare power generation set; and 4) new energy output and thermal power set the power grid are modified, and corresponding rotation spare optimal capacity under different new energy output with power transmission needs satisfied are calculated, and voltage stability margin-based power generation rotation spare capacity optimization is completed. With the method adopted, the optimization of power generation rotation spare capacity can be realized.