Because the traditional searching method of fault chains for cascading outages usually only consider the over-load protection or simulate the action of protection and control deterministically, a novel searching method of fault chains for power system cascading outages which is based on quantitative analysis of dynamic interaction between system and components is proposed. Based on fault chain model, an evaluating index is established. This index is used to quantize the action situation of protection and control of key elements. Furthermore, according to the index, the action probability of protection and control of key elements under critical condition is figured out to confirm subsequent events of fault chains for cascading outages. Finally, high risk fault chains are screened out based on the risk index. Taken some actual power system under the summer peak load condition in 2017 as an example, the simulation result proves reliability and effectiveness of the proposed method. This work is supported by Science and Techonology Project of Zhejiang Electric Power Company “Research on UHV AC/DC Power Grid Security and Stability Characteristics and Defense Capability for Severe Fault”.