When multiple Very High Frequency/Ultra High Frequency(VHF/UHF) airborne radios work simultaneously on the same airplane, there will be serious Electromagnetic Compatibility(EMC) problems of co-site interference, such as self-interference, intermodulation interference and crosstalk. Considering the case of three VHF/UHF radios on one airplane for air test, this paper analyzes the factors affecting the communication effect which contains antenna installation positions, air electromagnetic environment characteristics, spurious, intermodulation interference and others. After the comparison of electromagnetic environments between air and ground, the importance of the radio frequency components of spurious radiation and other related indicators of communication radio transmitters is preliminarily verified, and the influence degree of second-order intermodulation and third-order intermodulation caused by multi-radio communication in the same band or different bands is analyzed, which is helpful to guide the EMC design of VHF/UHF airborne radios.