Abstract: This paper presents an overmoded complex device of which the output power may approach 10 GW level without breakdown, derives self-consistently the phase lock equation of the radiation wave of the device driven by both the external electromagnetic signal and the prebunching electron beam simutaneously, and shows that when the phase is locked by the external electromagnetic signal and the prebunching electron beam simultaneously, the operation time reaching the phase lock can be shortened, the shift of the operation frequency to the locking frequency(the frequency of the external electromagnetic signal ) decreased, and the bandwidth of the phase lock operation enlarged.