Abstract: To enhance the operational capability of simultaneous transmit and receive(STAR) cognitive electronic warfare(CEW) jammer in the complex electromagnetic environment, an improved spectrum sensing scheme for cognitive jammer was proposed based on energy detection (ED), and the detection and false alarm probabilities in closed-form for the jamming target were derived. Simulation results show that the effect of STAR cognitive jammer receiver impacted by self-interference(SI) can be reduced by the proposed spectrum sensing scheme, which improves the cognitive capability of jammer for attacking target.