Abstract: The computer simulation from cold cavity to hot cavity of Hughes coupled cavity slowwave structure is depicted used by MAFIA. Cold cavity simulation result is compared with theoretical and experimental ones. The average error of dispersion is 0.02% and the average error of interaction impedance is 5%. So the simulation result is more consistent with experiment result than theory result. It may satisfy design precision requirement. Loaded in three dimension particleincell module in cold cavity simulation, the beamwave interaction simulation is done using by MAFIA software. The mechanism of beamwave interaction is qualitatively analyzed by software simulation.