The working medium adopted on the huge hydraulic close-die forging press both in China and abroad was introduced and the main physical-chemical properties of water (emulsions) and oil (hydraulic oil) used for hydraulic forging press, the technical interrelations between the working medium and components and the performance of direct-oil-pump-drive and water-pump-accumulator-drive were comparatively analyzed. The oil as working medium for China 800MN huge hydraulic close-die forging press was confirmed. Finally, the technical scheme and innovations for its hydraulic system were analyzed and studied from the aspects of reliability and safety, simulation and control etc..