A narrow band microwave pulse has been obtained experimentally by using a resonant cavity surrounding virtual cathode oscillation (vircator). There are several separate dominant modes with different frequencies in a resonant cavity. Although, the coupled coefficient of radial extracting slot and Q value for each mode are not the same, but to tune the virtual cathode oscillation by varying the diode voltage, so that its dominant frequency of free- running virtual cathode oscillation is near the passband of every mode in the resonant cavity, respectively, the several narrow band microwave pulses with different frequencies can be obtained. In our experiments, a cylindrical resonant cavity is used with the microwave power being extracted radially through circumferential a slot into rectangular waveguide, and the two narrow band single microwave pulses with different frequencies are observed. The resonant points of the cavity at 4.16 GHz and 5.13 GHz are selected. The measured frequencies of microwave are 4.14 GHz and 5.09 GHz with peak power of 1 approximately 4 MW, 3 dB bandwidth is 0.36% and 0.53% of the central frequency, respectively.