For high speed aircrafts radome, the performance of guidance system is often affected with thermal and mechanical loads changing its original electromagnetic characteristics under actual flight conditions. A Thermo-Mechanical-Electrical (TME) coupling model based on hexahedral mesh partitioning and a simulation method are proposed, and these two methods being employed, the effects of dielectric temperature drift and structural deformation on the electrical performances of radome at high-speed flight can be characterized accurately. First, based on the TME Sharing Mesh Model (TME-SMM), the temperature field of radome is obtained by transient thermal simulation, and the deformation field of radome is obtained by static analysis. And then, the dielectric temperature drift and structural deformation of radome are accurately transferred into its electromagnetic simulation model, and the electrical performance of radome is calculated by three-dimensional ray tracing method. Last, a typical example is utilized for simulating and analyzing the variation of the electrical performance of radome at high-speed flight. The results show that the variation is obvious, and the feasibility and research necessity of the method are further illustrated.