Abstract: A multi-path and multi-polarization propagation model for shortwave signals in the ionosphere was established. On this basis, numerical simulations were conducted to analyze the polarization states of shortwave signals transmitted from Wuhan under different conditions, including propagation through different ionospheric layers and propagation within the same layer at various elevation angles. The results show that circularly polarized waves evolve into elliptically polarized waves to varying degrees after exiting the ionosphere. Specifically, when transmitted southward, the F-layer induces more pronounced ellipticity; when transmitted westward, the E-layer leads to more significant ellipticity. For propagation within the E-layer, southward and westward transmissions exhibit only minor differences in ellipticity across different elevation angles. This model provides a theoretical foundation for single-station positioning and ionospheric detection using polarization antennas.