Abstract: The effects of resonator shape on the field uniformity in the reverberation chamber(RC)excited by high-power microwave(HPM)is studied.Firstly,the theoretical analysis of the electromagnetic modes in resonators shows that the resonator shape has important effects on the field uniformity.Then the statistical method named time-window is introduced to describe the characteristics of the transient field.Finally,the influences of the shape on the field distribution is researched by comparison of the maximum of electric field,the standard deviation and the isotropy characteristics in three kinds of resonators.The simulation results show that the resonator with complex configurations can reduce the standard deviation and improve the field uniformity efficiently.Thus it is capable to realize of the uniform electromagnetic environment in complex cavity.