To describe the nonlinear deformation of isotropic materials under non-isothermal loading, it is proposed to use the endochronic theory of thermoplasticity. In this study, the governing equations of this theory are obtained for the general case of loading and for the case of a plane stress state. The calculated dependences of the finite element method in relation to endochronic theory are given, and computational methods of solution are also presented. In the last part of the study, an example of calculating a thin plate under complex loading is considered.