Abstract: This paper analyzes the distribution and correlation of electrical field and magnetic field located at the emission domain in the solenoid for the high power foil less diode using over-mode microwave device based the single electronic moving equations.It is confirmed that the electronic beam transmission efficiency is correlated with the reflux.The results from experimental research indicate that distinct power efficiency was explicated for the emission electronic beam from foil less diode with different radius cathode when the guiding magnetic field inside the magnetic solenoid was bigger.When the beam radius was 48 mm the electronic beam transmission efficiency was more than 95%, when the beam radius was more than 90 mm the efficiency was smaller than 75%.