Abstract: On the basis of the nonlinear equations, the characteristic of nonlinear chaotic dynamics was investigated in a traveling-wave tube amplifier. The phase space of the electron orbits, the time-space distribution and the output power of the radiation field were studied numerically. The result shows the radiation field and the electron beam is a dissipative system. When the parameters such as current or detuning changes and are above a certain threshold, chaotic characteristic is appeared in the whole time and space of the system. The output power is characterized by the irregularly oscillation with the wide continuous spectrum.