A novel electromagnetic (EM) radiation regime, the plasma-based multistage virtual cathode radiation model is proposed. Recent study indicates that, as an electron beam passes through a high-dense ion background, due to the cooperation of the ion background and the modulation of the virtual cathode formed at the focusing point, a multistage virtual cathode can be formed. Further studies show that the electrons reflected at different stages of the virtual cathode will come into oscillation, and the EM radiation will be excited, which is different from the betatron emission in an ion channel. As an example, a beam-ion channel system bound in a cylindrical cavity is studied by using particle in cell simulation. It is confirmed that a multistage virtual cathode is formed and EM radiation is induced. Finally, the characteristics of the radiation are discussed in the present paper.