Abstract: UAV’s main telecontrol data link system is the main approach for battlefield air-ground communications. The antijamming performance directly affects the combat effectiveness of play. Continuous wave electromagnetic radiation tests showed that some sensitive frequency points easily lead interference on main telecontrol data link system of UAV. For further study of electromagnet? ic interference on coupling path and analysis of mechanism，a UAV is set as a subject for implementation using injection method. The re? sult shows that the front door is an important coupling path of continuous wave interference on main telecontrol data link system of UAV. Low attenuation of diplexer filter causes the jamming signal coupling into the internal operation of the circuit with the desired signal. The smaller the signal to noise ratio，the more interfering components superimposed with useful signal spectral components of BPSK modulation. The useful signal is suppressed and buried in the noise，so the error rate of the demodulator output is greater resulting in in? terference with normal communication and interruption to downlink telemetry link because of the poor isolation of the diplexer filter.