A new coaxialstructure SuperReltron was explored to develop a low impedance high power microwave tube. This source will have a power output of about 2.5GW with 25% efficiency at 52GHz, input modulate voltage is 125kV and post accelerating voltage is 600kV.Numerical simulations show that the frequency is approximately inversely proportional to the length of screen, and the scaling of output power is proportional to I2 ，　when the current is less than the space charge-limit ．