The GeSn photodetectors (PDs) have drawbacks such as the slow response speed and the poor signal-to-noise ratio. To overcome these disadvantages, we report one polarization-sensitive dual-mechanism-enhanced GeSn PD that contains both Fabry-Pérot (F-P) mode and Surface Plasmon Polaritons (SPP) mode. The F-P mode originates from the GeSn film assisted by an embedded SiO₂ film, while the SPP mode is associated to the added Au grating on the GeSn film. Simulation results show that these two types of modes can increase the optical absorption of GeSn from 20% to 80% at 2 000 nm. Moreover, under TM/TE polarization, absorption of the sample are 80% and 2.6%, respectively, and the extinction ratio is 31. Such a high extinction ratio indicates that the GeSn PD has great polarization selectivity. These results provide new ideas for the development of innovative GeSn PDs.