The present disclosure relates to an accelerating apparatus for a radiation device. The accelerating apparatus may include a plurality of acceleration cavity units including a plurality of acceleration cavities. Each of the plurality of acceleration cavity units may be configured to accelerate a radiation beam passing through an acceleration cavity. And the accelerating apparatus may further include a plurality of coupling cavity units each of which may include a coupling cavity. Two adjacent acceleration cavities may be electromagnetically coupled via the coupling cavity. The plurality of acceleration cavity units may have a plurality of holes each of which may be configured to be in fluidic communication with the corresponding coupling cavity. And an edge region of each of at least a portion of the plurality of holes may include continuously varying curvatures.