The invention discloses a control electrode assembly unit used in a cathode. The control electrode assembly unit comprises a control electrode module and an insulating cooling water pipe, and the control electrode module comprises a lead, a water cooling module and a control electrode. The water cooling module comprises a head cover, a water pipe connector, a lead connecting canister and insulating ceramics, wherein the water pipe connector, the lead connecting canister and the insulating ceramics are coaxially arranged in the head cover. One end of the insulating cooling water pipe is used as a cooling water inlet, the other end of the insulating water cooling pipe is connected with the water pipe connector, an opening which is communicated with an interior space and an exterior space of the insulating cooling water pipe is formed in the water pipe connector, the lead is arranged in the insulating cooling water pipe, one end of the lead is used as a signal input end, and the other end of the lead is connected with the lead connecting canister. According to the control electrode assembly unit used in the cathode, the cathode module and the crossed-field amplifier, extinguishing pulse signals are added on the control electrode through the lead, and the cooling water conducts cooling on the control electrode and the cathode at the same time. The cooling water pipe with an insulating medium is capable of making a bypass resistance between the control electrode and the cathode add one order of magnitude, thus guaranteeing that all the extinguishing pulse signals are added to the control electrode. In this way, the problem that sparking caused by a halfway extinguishing during pipe work is eliminated fundamentally, and reliability of the crossed-field amplifier is thus improved.