In order to address the issue regarding the disparity in the stability and responsiveness of the electro-hydraulic control system caused by the alteration of the properties of hydraulic oil within the deep-sea “high-pressure and low-temperature” environment, a test bench for a full ocean depth electro-hydraulic servo system utilizing a water-glycol medium was put forward. This system is capable of adapting to the changes in the characteristics of seawater at various seawater depths, particularly the high hydrostatic pressure present in the deep-sea environment, and can maintain high dynamic performance under diverse working conditions. This has a substantial influence on enhancing the motion control quality and stability of the electro-hydraulic servo system throughout the entire sea depth. It offers novel concepts for resolving the problems associated with hydraulic systems in the whole sea depth environment and lays a solid practical and theoretical foundation for improving China′s independent design capabilities of deep-sea equipment.