Interval analysis method is introduced to the static security analysis of power systems to deal with uncertainty of unit generation and load condition. Interval DC load flow algorithm is proposed to calculate load flow by solving interval linear equations after unit and branch outage. An improved confidence measurement function for comparing intervals in size is also presented. Based on those proposed， an interval method for automatic contingency selection（ACS） considering uncertainty in power system static security analysis is proposed and implemented. Finally， the proposed method is verified by three test systems: 5-bus test system， IEEE 14-bus test system and one provincial power system in China. By comparing the proposed method to the conventional method without consideration of uncertainty and probabilistic analysis， the paper demonstrates the necessity to take uncertainty into consideration in static security analysis and the effectiveness and applicability of the proposed method.