Abstract: The properties of plain carbon fabric prepreg were researched using a picture f rame shear rig which isinstalled on a mechanical test machine. The result shows that the shear properties of the fabric prepreg were similarto those of the pure fabric , which has different properties during different shear stages. According to the experimentdata , two-dimensional shear models were set up in two different shear stages. At the beginning of the shear stage ,a torsion spring was used to simulate the friction of the cross point of the warp and the wef t in the prepreg fabric.The torsion stiffness coefficient of the torsion spring was determined on experiment . In the second shear stage , therelationship of shear angle and load was given. It is proved that the torsion spring can simulate the shear f rictionwell in the first shear stage.