The subsurface imperfection is a measure cause for the drastic failure of the sandwich panel for many structural applications in aerospace industries. In this study the core defects in the woven glass fibre-epoxy face sheet and PVC foam sandwich structures were simulated for different shape and volume fraction for air voids. Cylindrical, spherical, cylinder with hemispherical ends (capsule) and rectangular shaped voids were considered for the finite element simulation. The volume fractions of voids were varied as 5, 7.5, 10, 12.5 and 15%. Three point bending test was simulated for a constant load to determine the deflection of the composite using Ansys. The displacement values were used to determine the flexural modulus, transverse shear rigidity and core shear modulus of respective sandwich-void configuration. The results show that as the volume fraction of the voids was increased, the central deflection was increased lineally and correspondingly the flexural modulus, transverse shear rigidity and core shear rigidity was decreased. The results shows that the % decrease in flexural modulus as compared with defect free PVC core for cylindrical voids was 9, 13, 17, 21 and 25 %; for spherical voids was 8, 12, 16, 20 and 23 %; for capsule voids was 9, 13, 18, 22 and 25.5 %; for rectangular voids was 12, 17, 20, 24 and 27 % corresponding to the 5, 7.5, 10, 12.5 and 15% void volume fractions, respectively. It was also seen that the % decrease in both the transverse shear rigidity and core shear modulus for cylindrical voids was 10, 15, 19, 24 and 27%; for spherical voids 9, 14, 18, 22 and 25%; for capsule voids 10, 15, 20, 24 and 28%; for rectangular voids 13, 18, 22, 26 and 29% corresponding to the 5, 7.5, 10, 12.5 and 15% void volume fractions, respectively.