| In this paper, the necessity and current methods of data exchange between CAD/CAE systems are discussed, and the research on the CAD/CAE integrated information model is summarized. This paper puts forward a STEP based Multi-Rigid Body Dynamics (MRBD) information model which incorporate the kinematic and dynamic features, gives a further development to CAD models, therefore resolves the problem rf data exchange between CAD syste ns and multi-body software for kinematic and dynamic analysis of mechanical systems using information models, contributing to the implementation of integration between CAD/CAE systems. MRBD information model is analyzed with STEP methodology and object-oriented technology. Parameterized design of kinematic and dynamic feature is done, and MRBD information is represented in formalization description language EXPRESS. An EXPRESS editor is developed under Visual C++, by which EXPRESS information models can be edited, compiled and mapped to C++ classes. These C++ codes, along with necessary functions that EXPRESS can not define, are helpful to develop software for STEP-based application. Multi-body dynamics is an important fundamental theory in studying sports biomechanics; therefore, MRBD information model is extended to the research of sports biomechanics. Motion mechanism and biomechanical property of muscle, factors influencing upon the calculation of muscle force are studied, then lubrication mechanism of articulation and biomechanical models of knee are discussed. Friction model of articulation and 3D biomechanical model of human knee-joint including patella are built. Main parameters of muscle force, ligament force and articulation contact force are extracted and analyzed, at last the EXPRESS models of these forces are established. STEP is a developing standard, in allusion to that kinematics and dynamics feature is a blank in the current CAD models, STEP-based MRBD model is set up in this paper, which will promote the development of STEP.
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