Abstract: From the perspective of micromechanics, taking into account the in-plane fiber bending and resin-rich defect, an unit cell model was established for stitch damage of the stitching reinforcement for composite laminates containing a large circular hole. The fiber bending function was established and the fiber volume content and fiber bending angle of the fiber bending region were deduced. By applying the method of mechanical analysis of composite materials, the elastic constant of the unit cell was calculated. The study shows that the maximum bending angle of the fibers in the cell surface is never over 20°, the longitudinal Young's modulus decreases while the transverse Young's modulus, shear modulus, and Poisson's ratio increase by not more than -8%-20%; as for composite laminates containing a large circular hole, the variation in material properties caused by changes in needle span is much greater, compared with the edge distance. Based on the calculation results above, a new method for calculating the mechanical properties of the stitching reinforcement for the composite laminates containing a large hole was established. Simultaneously, stitch holes were used to simulate the stress concentration at the stitching. The study results reveal that the stitching may lead to the decrease of the laminates' in-plane mechanical properties, and there is a much stronger influence on the in-plane compress performance than the one of in-plane tensile properties.