Abstract: To address the issue of uncharacterized path loss and shadow fading of off-body channels in the terahertz band of wireless body area networks, the THz off-body channel characteristics based on measurements were studied. The CI (Close-In) and FI (Floating-Intercept) path loss models were constructed, and the off-off body channel shadow fading was characterized using modified Kirchhoff and METIS knife-edge models. Measured on-off body and off-off body scenario channel data in the 129.5–135 GHz frequency range were combined, and an in-depth study of path loss and shadow fading characteristics for off-body channels was conducted. The results show that the FI model accurately describes on-off body channel path loss with an RMSE of 0.219 against measured values, and that the modified Kirchhoff knife-edge model can effectively represent human body shadow fading. These results provide theoretical support for the design and optimization of THz off-body communication systems.