In this paper, the radiation characteristics of a slot annenna in conduction cylinder covered with a moving isotropic plasma layer are analyzed. Integral representations of the eletromagnetic fields in the spectral domain radiated through the plasma layer are derived and converted into the fields in the spacial domain by saddle-point ingegration. Radiation null which brings about distorion in the radiation parrern is explained by the zero of integrand in an asymptotic integral as a function of plasma and velocity parameters. Numerical results for a radiation null calculated from various plasma and velocity parameters correspond to the results of planner structure.