in this paper a new method is introduced for evaluating effect of sweep noisy barrage jammer on tracking radars. In this method, jammer interfering energy that injected in radar receiver bandwidth is calculated during jammer scan period, then according to the minimum signal to jammer power ratio that is required for receiver proper functioning, ratio of receiver proper functioning time to the jamming scan period or ratio of receiver destruction time to the jammer scan period is determined. These parameters are more important than only presence of jammer in receiver bandwidth. We define new performance criteria to evaluate the jammer effect on tracking radars. This is done by considering ratio of receiver destruction time to jammer scan period and the ratio of received power from the jammer to received power from the target at receiver front end.