In this paper, a new high power and wideband amplifier with permanent periodic magnet(PPM) focusing is presented. It consists of klystron and FEM . Focusing, bunching and emiting of the electron beam in this device are studied theoretically. The radiation parameters of the device have been estimated as the frequency is 11.4GHz, output power 18MW and output bandwidth rate 44% at the conditions in which a order of modulating coefficiency is 30% of the klystron, radius of the waveguide 1.51cm, the amplitude 0.16T and period 7.92cm of the magnetic field of the wiggler, and the voltage is 490kV, current 50A and radius 0.368cm of the electron beam.