A dynamic simulation and analysis system for sophisicated electro-hydraulic circuits ( called “HYCAS” ) was developed by KUBOTA for performance estimation and parameter optimization. The structure consisting of six fundamental functions and simple interactive operation makes the system a more convenient and practical CAE tool for design engineers and researchers. The main features are as follows. 1) A hydraulic circuit is constructed in a manner similar to CAD using standardized component graphic symbols. 2) The connection to the mechanical system and electrical system containing feedback signals is possible. 3) A target simulation program is automatically generated by the original algorithm based on its structure. 4) Any dyanmic output data in the circuit is easily selected and evaluated by the convenient post-processor functions. 5) In addition to the the above main function, the auxiliary function and retrievable database are provided to facilitate easy addition and modification of symbols, models and parts data. “HYCAS” has been applied to various tractor electro-hydraulic circuits. The specific application of a tractor 3-point hitch control is discussed to demonstrate the effectiveness of this system.