A special electro hydraulic servo system was developed for precise control of parallel two-stage cylinders in order to drive model supporting mechanism in a large wind tunnel. Many ingenious designs were introduced in oil source system,servo controller system and electric control system of the new special electro hydraulic servo system. Not only the needs of large inertia, heavy load, and large flow span special condition are met, but also the pivotal problems of controllability of super-large area ratio cylinder, synchronous ability and precise location ability of parallel two-stage cylinders, and security of system operation can be solved well.