Abstract: In order to evaluate the anti-electromagnetic interference performance of radar equipment, based on the mechanism of pseudo-signal interference effect of electromagnetic radiation, the relationship between the contribution of out-of-band multi-frequency third-order intermodulation signal and in-band single-frequency pseudo-signal interference effect is clarified, and the concept of pseudo-signal interference effect index is introduced. The evaluation model of third-order intermodulation pseudo-signal interference effect is established, and the model correction method and effect test prediction process are proposed based on the change rule of pseudo-signal level value. Taking a stepped-frequency continuous wave ranging radar as the research object, the out-of-band third-order intermodulation critical pseudo-signal interference effect test of the tested radar is carried out by using the method of differential mode injection equivalent substitution of electromagnetic radiation. The results show that the influence of the third-order intermodulation pseudo-signal interference increases first and then decreases with the increase of the radiation frequency offset in the range of 0.2–2.2 GHz on both sides of the radar working center frequency. The experimental verification is carried out by changing the interference frequency point, field strength combination and pseudo-signal sensitive level. It is proved that the accuracy of the third-order intermodulation pseudo-signal interference model is better than 2 dB, which can objectively evaluate the third-order intermodulation pseudo-signal interference of radar equipment.