Abstract: Noise-jammer can be used to combat active and passive sonar search and tracking.In this paper,the ratio between the operating distances after and before the sonar being suppressed is used as a parameter to establish the model computing the suppression region created by noise-jammer.The shortcut curve function is defined,and the modle of computing the shortcut curve function and the effective search width is also set up.The effects of noise-jammer on suppressing sonar can be evaluated by computing the effective search widths before and after suppression and the variation of the noise-jammer’s effective search width at different position.