Abstract: In order to improve the electromagnetic protection capability of radar equipment, the two types of pseudo-signal interference imaging mechanism of radar equipment are revealed based on the working principle of stepper-frequency radar ranging for the problem of pseudo-signal formation on the radar display interface when typical radar equipment is subjected to single-frequency electromagnetic radiation, thus causing misjudgment of real targets. With a type of Ku-band step-frequency ranging radar as the test object, a single-frequency electromagnetic radiation pseudo-signal interference effect test was carried out to verify the correctness of the two types of pseudo-signal interference imaging mechanism analysis. The variation curves of the two types of pseudo-signal level values with single-frequency interference field strength at typical frequency points in and out of the band are obtained experimentally, and the variation laws of the pseudo-signal level values in and out of the band are explained respectively based on the nonlinear distortion analysis of the receiver circuit, and then the sensitive frequency bands of the two types of pseudo-signal interference are measured. The test results show that: In-band single-frequency electromagnetic radiation can cause "pulse" type pseudo-signal interference to stepper frequency radar equipment, the location of the pseudo-signal is random; out-of-band single-frequency electromagnetic radiation can cause "impulse" type pseudo-signal interference to stepper frequency radar equipment, the location of the pseudo-signal is fixed; as the single-frequency interference field strength increases, the "pulse" type pseudo-signal level value first increases linearly, and then remains constant, the "impulse" type pseudo-signal level value first gradually increases, reaches the maximum value and then gradually decreases.