Abstract: The servosystem of a flight motion simulator requires its servovalve-motor combination to possess a great ratio of continuous adjustable rate （e. g. more than 1100）. In general, only the electrohydraulic servosystem is available to the simulator with a great load inertia （e. g. 30 kg.cm.sec2）. This paper presents a new complex electrohydraulic system, which increases the ratio of adjustable rates from 180 to about 1800 and improves other technical performances so as to meet the requirements of the servosystem in the flight motion simulator.- The paper lists some ratios of adjustable rates of domestic servomotors used in simulators, analyses the reasons of the low ratio of adjustable rates of the piston type motor and puts forward some measures to improve it. The paper also describes the principles of the complex electrohydraulic servosystem, gives the theoretical analysis and derives the block diagrams and transfer functions. Then, it Rives the dynamic analysis of the complex system and makes a comparison with the original one. Finally, it provides the typical data and plots of experiments.