Based on the management and assessment system about power plants， this paper introduces the system construction firstly， then a new AGC compensation algorithm is illustrated according to the comprehensive performance index and regulation amount. Multiplication of response time， regulation speed and precision indices makes the compensation more reasonable with the consideration of the turn-back parameter. System application shows that this algorithm can assess the amount of AGC compensation precisely and effectively， and motivates the plants to improve AGC performance and participate in AGC regulation.