Abstract: Employing the concept of cognition into radar jamming, the jamming system can implement behavior learning in the dynamic jamming process, which can ensure the most suitable jamming plan scheduling and then achieve the most efficient jamming effect. The concept and connotation of cognitive radar countermeasure were discussed firstly in this paper. Then the cognitive radar ECM process flow was devised based on <i<Q</i<-learning algorithm and the key techniques in the cognitive jamming process were brought forward. At last, the verifying simulations of convergence of the cognitive ECM process and the performance improvement with prior information were presented.