A frequency analysis system for single short microwave pulse which is developed by means of a ring of waveguide dispersive line is described in this paper.The system is characterized by frequency resolution 6 times higher than that of normal dispersive line with the same length.At the same time,the ring of dispersive line is capable of measuring the time-dependence realation for microwave frequency components and avoides uncertain rising from the duration of microwave pulse,making the uncertain is less than 2％.The system has been used successfully in the experimental study of Vircator．