The invention discloses a system and a method for evaluating importance of power system facilities. The system for evaluating importance of the power system facilities utilizes a C/S (client/server)-architecture client side program and a background relation data base. The client side program comprises a power system Monte Carlo simulation module and a risk evaluation module, the power system Monte Carlo simulation samples running states of each facility randomly, analyzes power flow and node voltage of the power system after confirming running states of the power system, judges whether the running states of the current power system meet the corresponding restraints or not, and if not, simulating rescheduling of the power system so as to define the minimum load capacity. The risk evaluation module is used for evaluating running risks of the power grid on the aspects of economy, safety and environment and the like quantitatively in the running state of the current system, and the background relation data base is used for storing original data and calculation results and statistics and summarizing of simulation results.