Abstract: Underwater pumped hydro storage (UPHS) is a novel energy storage method suitable for marine environments. To address the problem of imprecise UPHS models and limited applicability, this study presents a hydraulic-mechanical- electrical multilink transient model and conducts associated research. Firstly, we analyze and establish the physical model of UPHS components, including the pump-turbine, governor, motor, and converter. Subsequently, we design the control strategies for the prime mover and grid-connected converter. Finally, this paper performs electromagnetic transient simulations for stand-alone grid-connected UPHS and offshore wind power-UPHS bundling transmission scenarios under various working conditions. Simulation results confirm the model's reliability and demonstrate that underwater pumped hydro storage is feasible for smoothing offshore wind output power.