As a novel concept of vircator geometry proposed in this paper, the outward-emitting coaxial vircator (OECV) is at the cutting edge in the field of high-power microwave (HPM) source researches. Theoretical analyses are carried out to study the space-charge-limiting current in coaxial configuration and the terms of virtual cathode formation. According to the simulation results, OECV has the advantages in energy conversion efficiency and bears the potentialities in increasing the high-power microwave pulse width, as well as in generating HPM in relatively low bands. Two kinds of geomtries for HPM emission are also given in this paper.