Point defects are implanted in an ordered granular system by randomly selecting granules and changing their stiffness coefficients. The discrete element method is used to research the normal force probability distribution. Simulation result shows that force network is almost homogeneous without defects whereas force network will become inhomogeneous with defects. The concepts of primary normal force and secondary normal force are proposed and their statistics are analyzed separately. As the rate of defects increases, the changing process of primary normal force distribution is complex, whereas the secondary normal force distribution is always exponential distribution. Our simulation shows that normal force distributions are different between randomly packing system and compositional disordered system of low defect rate. But when defect rate is large, the distributions are similar. These results are beneficial to the understanding of the relationship between inhomogeneous force network and disordered system.