Abstract: A new type of test system has been designed for the research on microwave radiation characteristics of large-aperture antenna excited by short pulses. The system is made of a pulse-width tuning microwave source (the shortest pulse-width is 0.5 ns) and a receiving system whose dynamic range is up to 52 dB. Based on such test system, the changing curve of antenna pattern and the pulse-width of antennas radiation field waveform were obtained under the condition of different microwave pulse-width. The results show that in far field, there is no significant influence on the radiation waveform in the principal axis, by changing microwave pulse-width; it was found that radiation waveforms deviated from the principal axis in different angles could present pulse widening and amplitude decreasing, the greater the angle deviated, the more obvious the phenomenon could be.