The invention discloses an automatic power generation control performance evaluation method and system based on amplitude change. The method comprises the steps: obtaining each time sequence in actualpower and expected active power, and dividing the time sequences into K data segments; respectively calculating amplitude changes of the actual power and the expected active power; judging whether the absolute value of the difference of the two is smaller than or equal to a threshold value of significant amplitude change of the actual power and the expected active power or not; if yes, the AGC performance is ideal; otherwise, the AGC performance is not ideal, and dividing the amplitude changes into a plurality of abnormal conditions according to the amplitude changes and the threshold value.The method has the beneficial effects that by calculating the threshold value of the significant amplitude change, the false detection frequency under the poor performance condition is reduced; amplitude changes are divided into six abnormal conditions, and additional information is provided for processing the abnormal conditions.