Abstract: Based on the frequency diversity basic theory, compared with single frequency radar, the counter-jamming effectiveness for frequency diversity radar is analysed and modeled. The model includs counter-jamming improvement factors, radar detection range and detection probability. The models analysis concluds that the frequency diversity radar couldn't improve the received signal-to-jam ratio with the same total power. The reason of frequency diversity radar can weaken jamming effectiveness is that it can improve the reliability of radar, not the detection capability.