A new high power microwave source,the axial acceletron is presented in this paper.　Compared with the radial acceletron,　an acceleration region is added after the diode/oscillator and radial acceleration is changed to　axial acceleration.The bunching and radiation of the electron beam in the device are investigated.　It is found that the electron beam may approach ideal bunching, each harmonic current of the beam may reach about 5.6 times of the initial direct current in the nonrelativistic regime.　High power microwave pulses with tunable frequency can be generated by postaccelerating the electron beam and carefully designing the extraction cavity.