Closed-loop discrete control is the main means for maintaining operational reliability of power systems subject to large disturbance， which includes fault-driven emergency control and trajectory-driven corrective control. This paper compares the criterion， execution time， precision and cost of the two control strategies， as well as their generator tripping， load shedding and network splitting actions. If an emergency control is used to cope with uncertain factors occurring in small probability and high risk， it will most likely lead to over-controlled results in most of operational scenarios. If correction control is used in this case to cope with the factors that have a large probability to occur， the opportunity cost would be high. Based on the risk analysis to emphasize a compromise between these two control strategies with consideration of their physical and economic characteristics， this paper proposes a method using decoupling-optimization and global-coordination to find a minimum risk solution.