Using the structure of the coaxial vircator oscillator, a new kind of compact radial split-cavity oscillator is presented. The characteristic of the oscillator is that the input current can be intense, and this is the main reason for the output microwave power to be high. Taking into consideration all kinds of factor, under the condition of the voltage of 410kV and the beam current of 35kA, the numerical simulation gives an average output microwave power of about 50GW at the microwave frequency of 146GHz, and the electronic efficiency is 348%.