Abstract: The existing assessment method for AGC can be improved through analyzing the complexity of AGC signals of Units. In this paper, by taking the control performance of generation unit into consideration, the complexity characteristics of AGC signals is studied. By using the mathematical model of the CCS for generation unit, the control performance of power plant under different AGC orders is analyzed, and a quantitative analysis method for complexity is put forward, which is suitable for discrete and continuous AGC orders. The concept of average steady-state load point is put forward to adapt to the situation of the variety of load points when units operate. Results show that the complexity characteristics of AGC orders depend on its characteristics. Based on the AGC order data for a 1 000MW unit, the simulation and analysis are carried out from such aspects as day and month scales. The results show that the method can effectively realize AGC signals analysis on complexity characteristics, which provides classification base for generation mission degree of units.