Through the observation of photomicrographs of resin regions around Z-pin ends, the basic hypothesis of the elliptic configuration of resin regions in the X-cor sandwich were proposed. The parametric equations for describing the microscopic structures of resin regions were given. Then the geometric analysis model of X-cor sandwich was established. The finite element software ANSYS was used to establish the finite element model of the shear modulus and the shear modulus was calculated. The error range of finite element analysis is between ±10%. So the rationality of finite element model is verified and the finite element model can be used to forecast the shear modulus.