Abstract: Using plasma fluid theory, from linear perturbation equations, the effect of the beam current size on the dispersion relation of plasma-filled dielectric Cherenkov maser is examined when the beam current is complete, or not effectively neutralized by the return current in the background plasma. The dispersion relation and the wave growth of the TM0n are solved under both cases. Based on this, a discussion on the effect of the beam current on the dispersion relation and wave growth is given. Both of the cases of plasma return current can or not effectively neutralized electron beams current has different dispersion relation and wave growth. When the parameters of waveguide and plasma are fixed, the electron beam current is not the bigger the better, too large electron beam current is harmful for improving the efficiency of the device, and there has an optimal matching relationship between them.