The invention discloses a traveling-wave tube internal temperature soft-measurement method based on a finite element model. With multi-point temperature values of the shell of a traveling-wave tube as auxiliary variables, the finite element soft-measurement thermal model of the traveling-wave tube is created; with heat source distribution as independent variables, a target function of an error sum of squares between the multi-point temperature measurement values of the shell and corresponding point temperature simulation values of the finite element thermal model of the traveling-wave tube is derived, and is solved by an iterative algorithm, so that an optimal heat source distribution solution is obtained, finally, the optimal heat source distribution solution is loaded into the finite element thermal model of the traveling-wave tube, and an internal temperature soft-measurement value of the traveling-wave tube is obtained by finite element stimulation calculation. The traveling-wave tube internal temperature soft-measurement method based on the finite element model breaks through the limitation of conventional detection, and prevents a series of complex problems brought about by temperature sensors placed in traveling-wave tubes, measurement is convenient, the implementation cost is low, and the traveling-wave tube internal temperature soft-measurement method based on the finite element model can be applied in the mass testing of traveling-wave tubes.