Large-scale wind power adds significant uncertainty to the system equivalent load.The uncertainty requires more substantial day-ahead spinning reserve if traditional unit commitment strategy is still used，which results in significantly higher operational cost.Based on the small probability characteristics of the extra reserve demanded to cater for the wind power uncertainty and the characteristics of wind power forecast error decreasing gradually with time scales，a new multi-level unit commitment strategy is proposed.In the day-ahead unit commitment，the economy can be improved by relaxing power supply reliability.If the spinning reserve cannot meet the actual demand in the system operation，the unit commitment scheme should be adjusted through the secondary and tertiary unit commitment.Thus the combination would reduce the operational cost on the premise of ensuring system reliability and security.Simulation results of a province power system show that the operational cost is reduced and the effect is more significant with higher wind power penetration.